epoxy/2d materials aerogel composites with multifunctional

Epoxy2D materials aerogel composites with

multifunctional properties

A thesis submit to

The University of Manchester

for the degree of

Doctor of Philosophy

in the

Faculty of Science and Engineering

2021

Pei Yang

Department of Materials

School of Natural Sciences

2

Contents

Contents 2

List of Tables 6

List of Figures 8

List of Abbreviations 18

List of Pubilications 19

Abstract 20

Declaration 21

Copyright 22

Acknowledgments 23

1 Chapter 1 Introduction 24

11 Polymer materials 24

12 2D materials 25

121 Graphene 25

122 MXene 27

123 Other 2D material 29

13 Polymer nanocomposites 29

131 Nanocomposites with 2D materials 30

132 Epoxy2D materials based nanocomposites 30

133 Aims and objectives 31

2 Chapter 2 Literature Review 36

21 Preparation of 2D materials-based aerogel 36

211 Hydrothermal reduction method 36

212 Cross-linking method 40

213 Chemical reduction method 42

214 Ice-template method 44

22 Preparation of 2D materials aerogel-based polymer nanocomposites 51

3

221 Dip coating 51

222 Casting approach 52

223 Electrostatic spray deposition 52

224 Vacuum infiltration technique 53

23 Properties of 2D aerogel-based polymer composites 54

231 Electrical properties 54

232 Thermal properties 56

233 Joule heating properties 60

234 Mechanical properties 62

235 Other properties 64

24 Potential application of 2D materials aerogel-based polymer composites 65

25 Conclusion 66

3 Chapter 3 Ice-templated hybrid graphene oxide - graphene nanoplatelet lamellar

architectures with tunable mechanical and electrical properties 67

31 Introduction 67

32 Materials and methods 69

321 Materials 69

322 Synthesis of Graphene Oxide 69

323 Production of the rGO-GNP Aerogels 71

324 Zeta potential characterisation 72

325 Morphylogy and microstructure 72



33 Results and Discussion 73

331 Rheology of suspension as a function of chemical reduction time 73

332 Production of areogels 76

34 Conclusion 86

4 Chapter 4 rGOGNP aerogel based epoxy composites for Joule heating applications

88

4

41 Introduction 89

42 Experimental methodology 90

421 Materials 90

422 Synthesis of aerogel composite 90

423 Joule heating characterisation 92

424 Morphology and structure 93

425 Electrical and thermal properties 93


43 Results and discussions 94

431 Morphological and structural analysis 94





44 Conclusion 107

5 Chapter 5 Hierarchical graphene aerogel interpenetrated-carbon fibre polymer

composites 109

51 Introduction 109

52 Experimental 111

521 Materials 111

522 Preparation of the reduced graphene oxide aerogel reinforced carbon fibre

(rGOA-CF) composites 111


524 Morphology and microstructure 113



53 Results and discussion 114

531 GO and rGO powders 114

532 GOA-CF and GOA-CFEP composites 115

5



535 Fracture toughness enhancement of the composites 121

54 Conclusion 125

6 Chapter 6 Epoxy resinTi3C2Tx MXene Aerogel Composites for Electrothermal

Applications 127

61 Introduction 127

62 Experimental section 128

621 Materials 128

622 Preparation of Ti3C2Tx 128

623 Preparation of 3D Epoxy resinTi3C2Tx MXene Aerogel composites 129




63 Result and Discussion 133

631 Morphological analysis 133

632 X-ray diffraction studies 134

633 Electrical conductivity 135

634 X-ray photoelectron spectroscopic result 137

635 Joule heating characteristion 140

64 Conclusion 149

7 Chapter 7 Conclusions and Future Work 151

71 Conclusions 151

72 Future work 156

References 158

6

List of Tables

Table 2-1 Summary of properties and applications of 2D materials aerogel based polymer

composites 66

Table 3-1 Summary of processing parameters samples density samples volume shrinkage

(before and after freeze dry) and XPS spectroscopy result of C1s spectra and O1s

spectrum for CR0 CRtTR300 and CR60TR800 aerogels 77

Table 4-1 Summarized sample loading and starting graphene suspension concentration

91

Table 4-2 Electrical conductivities of EGAC samples compare with reported graphene-

basedEP composites 98

Table 5-1 Density of CFEP Oven-dried GO-CFEP GOA-CFEP and rGOA-CFEP

composites 117

Table 5-2 Electrical conductivities of rGOA-CFEP compare with reported graphene-

basedCF composites 120

Table 5-3 Mechanical properties of rGOA-CFEP compare with reported graphene-


Table 6-1 Extracted fitting parameters of epoxy resinTi3C2TX aerogel composite before

Joule Heating test 139

Table 6-2 Extracted characteristic parameters (120591 g 120591 d and hr+c) for the Joule heating

performance of epoxy resinTi3C2Tx aerogel composite at different applied voltages

146

Table 6-3 The extracted parameters from XPS analysis of bare Ti3C2TX MXene aerogel

and epoxy resin Ti3C2TX MXene aerogel composite 149

Table 7-1 Joule heating properties comparison between rGOGNP aerogel epoxy

composites and MXene aerogel epoxy composites 153

Table 7-2 Joule heating features of epoxy resingraphene-based aerogel composite with

reported electrothermal materials (l length b breadth and h height) 154

Table 7-3 Joule heating features of Ti3C2TX aerogel and epoxy resin Ti3C2TX MXene-

7

based aerogel composites with reported electrothermal materials (l length b breadth

and h height) 155

8

List of Figures

Figure 11 Molecular structure of epoxide group 24

Figure 12 (a) Different kinds of the studies 2D nanomaterials[8] (b) Research

development of 2D nanomaterials[9] 25

Figure 13 A molecular model of a single layer of graphene[10] 26

Figure 14 (a) General schematic of the explanation of the formation of MXene from the

corresponding MAX phases [25] (b) Schematic of the process of Mo2CTx synthesis

by etching the selected two Ga layers from Mo2Ga2C (purple green brown red and

white represent of Mo Ga C O and H atom respectively) (c) SEM images of

MXene flakes[20] 28

Figure 21 (a) Photographs of 2 mgmL GO dispersion before and after hydrothermal

reduction at 180 degC for 12 h (b) photographs of GO hydrogel allowing easy handling

and supporting weight (c-e) SEM images with low and high magnifications of rGO

hydrogel microstructures (f) room temperature I-V curve of the rGO hydrogel

exhibiting Ohmic characteristic (insert for showing a two-probe method for the

conductivity measurements)[60] 37

Figure 22 XRD patterns of natural graphite (black) GO (blue) and freeze-dried rGO

aerogel[60] 38

Figure 23 (a) Poissonrsquos ratio in the air as a function of applied strain in the axial direction

(b) Poissonrsquos ratio with a function of numbers of compression and release cycles

along the axial direction (Blue and black are Poissonrsquos ratios when the aerogel is in

air and acetone respectively) (c) The Schwartzite model for sp2-carbon phases used

for the Poissonrsquos ratio modelling[76] 39

Figure 24 (a) Fabrication process for the 3D Fe3O4N-GAs catalyst stable suspension of

GO iron ions and PPy dispersed in a vial (b) Fe- and PPy-supporting graphene

hybrid hydrogel prepared by hydrothermal self-assembly and floating on water in a

vial and its ideal assembled model (c) monolithic Fe3O4N-GAs hybrid aerogel

obtained after freeze-drying and thermal treatment (de) typical SEM images of

9

Fe3O4 N-GAs revealing the 3D macroporous structure and uniform distribution of

Fe3O4 NPs in the GAs(f) schematic diagram of the morphological formation of

highly porous Gas[82ndash84] 40

Figure 25 (a) Photographs of the processing for ultralight N-doped rGO aerogels (b) SEM

image for rGO aerogels (c) electrical conductivity of rGO aerogel with the functional

of compressive force[87] 41

Figure 26 Schematic presentation of the synthesis procedure for the glucose strutted

graphene aerogel paper[93] 42

Figure 27 (a) Digital photos of the aqueous suspension of graphene oxide (b) heating the

mixture of graphene oxide and Vitamin C without stirring (c) The final aerogel after

CO2 dried (left) and freeze-dried (right) (d) A 71 mg graphene aerogel pillar with

the diameter of 062 cm and the height of 083 cm supporting 100 g counterpoise

more than 14000 times its own weight[98] 43

Figure 28 SEM images of supercritical CO2 dried (a) and freeze-dried (b) graphene

aerogels and typical nitrogen sorption isotherms (c) BJH (BarretndashJoynerndashHalenda)

desorption pore size distribution (d) of these graphene aerogels[85] 44

Figure 29 (a) Qualitative schematic of the relationship between nucleation and crystal

growth as a function of freezing temperature during ice solidification (b)

Performance of water absorptionresistance on the cross-section of a sponge[103]

45

Figure 210 (a) Parallel to freezing direction and (b) top view (perpendicular to freezing

direction) of a GO-PN fabricated by freeze casting of GO-sus (c) Foam-like porous

networks fabricated by using high concentrated oil-in-water emulsions (75 vol )

and (d) hybrid foam-lamellar structure fabricated through the freeze casting of oil in

water emulsions with low oil content (25 vol ) (e) A lamellar GO-PN produced

from GO-sus of the same density (5thinspmgml) as those used for samples shown in (ab)

but using smaller GO flakes (lt2thinspμm) than (ab) (20ndash60thinspμm) (f) An rGO-PN network

after the heat treatment at 1223K[105] 46

Figure 211 Illustration of a radiating graphene oxide aerogel fabricated by bidirectional

10

freezing (a) Scheme of the fabrication process (b) The freezing set up for making

the radiating structure has a copper rod with its upper surface hollowed out (c) Two

temperature gradients are induced by the upper copper mold (d) Model of the ice

crystals growing along with radial directions because of the two temperature

gradients The orange sheets represent the dispersed graphene oxide sheets[106] 47

Figure 212 Optical and SEM images of GO aerogels made by adding different additives

and comparison of BDF with conventional freezing methods (a) Ultralow density

(69 mg cmminus3 ) rGO aerogel made by adding ethanol during freezing standing on

grass (b) rGO aerogel with a weight of 27 mg can sustain 290 g of iron blocks (c)

rGOcellulose nanofiber (CeNF) nanocomposite aerogel with an obvious radiating

pattern on its surface (d) GOchitosan aerogel without chemical reduction one can

also see the texture on the surface (e) SEM image of the rG-OCeNF nanocomposite

aerogel (fg) SEM images of GOchitosan aerogels even a spiral pattern can be

obtained (hminusj) Illustrations comparing BDF and conventional freezing methods

using three cylindrical molds projected to the plane of the paper[106] 48

Figure 213 Schematics and images of the fabrication strategy to produce Ti3C2Tx

aerogels and supercapacitor electrodes by using three different approaches From the

top left of the image following the arrows optical photographs and SEM images of

Ti3AlC2 particles the image of the mold on top of the freeze caster containing the

Ti3C2Tx suspension (aqueous suspensions is schematically illustrated) and

corresponding SEM image of a few layers sheet unidirectional freeze-cast sample

inside the mold (schematic of the microstructure formation during ice crystal growth)

optical photographs and SEM images of electrode layers in the form of as-prepared

MA (lamellae architecture formed within the aerogel is schematically illustrated)

pressed (P-MA) and rolled Ti3C2Tx aerogel (R-MA) The range of electrode densities

(ρ) achieved by each approach is also indicated The red vectors inserted in the SEM

images indicate the freezing direction[107] 50

Figure 214 (a-d) Processing of dip-coating method for graphene aerogel-polymer

composites[110] 52

11

Figure 215 Schematic of the electrostatic spray coating process[111] 53

Figure 216 The processing of vacuum infiltration technique (UGA Unidirectional

graphene aerogel)[52] 53

Figure 217 (a) Electrical conductivities of GAepoxy composites as a function of GO

concentration (b) DC electrical conductivities of GAepoxy composites in the

alignment direction and transverse to it [112] 54

Figure 218 The electrical conductivity of NOGA-epoxy composites in orthogonal

directions at different NOGF content[113] 56

Figure 220 Scheme of thermal and electron transport in composites reinforced with 1D

2D and 3D graphene foam[110] 56

Figure 221 Thermal conductivity of PI and 035 wt graphene aerogelPI at 150 degC and

PDMS and 07 wt graphene aerogelPDMS at 85 degC[110] 58

Figure 222 Thermal conductivity vs filler content of Polyamidegraphene aerogel

Multigraphene flakesPDMS Multigraphene flakesgraphene aerogelPDMS[110]

59

Figure 223 Thermal conductivity of raw BN epoxy composites raw BN-rGO epoxy

composites and 3D BN-rGO epoxy composites with different filler loading [119]

60

Figure 224 (a) Heating profiles of GrFminusPDMS composite as a function of increasing

currents (at room temperature 25 degC) (b) Heating profile of the 01 vol

GrFminusPDMS composite at room temperature and input current of 04 A (c) Schematic

representation of restricted phonon transport is poorly dispersed conductive filler

composites vs uninterrupted phonon transport in GrF[120] 61

Figure 225 Joule heating test for 3D MXene aerogel-based polymer composites [109]

62

Figure 226 Mechanical properties of GA-epoxy composites (a) Flexural modulus and

strength and (b) fracture toughness of GA-epoxy composites as a function of

graphene content[113] 63

Figure 227 Typical SEM images of fracture surface for (a) neat epoxy and epoxy

12

composites with (b) 004 vol (c) 011 vol and (d) 022 vol UL-UGA aligned

against the crack plane (e) fracture toughness of UL-UGA and S-UGAepoxy

composites SEM image of fracture surface of S-UGA composite with (f) 016 vol

(g) 004 vol (h) 007 vol and (i) 011 vol of UL-UGA[112] 64

Figure 31 Schematic of the processing route towards rGO-GNP lamellar aerogels (First

row schematic of processing route for rGO-GNP lamellar aerogels Second row

Details of processing from frozen structure to rGO-GNP lamellar aerogel) From left

to right GNP is incorporated into GO aqueous suspensions via shear mixing the

GO-GNP suspensions are partially reduced with L-ascorbic acid at 50 degC for different

times t these are subsequently freeze casted and dried to form lamellae structures

templated by the ice crystals after a freeze-drying step the aerogels are subjected to

a final thermal treatment at 300 and 800 degC in Ar 69

Figure 32 SEM images of (a) graphene oxide (GO) flakes and (c) graphene nanoplatelet

(GNP) flakes (both with flakes width distribution) 70

Figure 33 AFM images of (a) graphene oxide (GO) flakes and (b) graphene nanoplatelet

(GNP) flakes 71

Figure 34 Digital images of GO-GNP suspensions as-prepared CR0 (a) after 35 min

CR35 (b) and after 60 minutes CR60 (c) of the chemical reaction Insets show a

magnified digital image of a droplet of the respective suspension on a 45deg inclined

glass slide after 60 minutes 74

Figure 35 (a) Viscosity (Shear rate at 1 S-1) and (b) as-measure pH value of GO-GNP

suspensions for different chemical reduction time (at 50 degC) The pH value of a

suspension upon the addition of with no chemical reduction step is indicated with the

half-filled symbol in (b) The corresponding zeta potential values of GO-GNP

suspensions at 5 35 and 60 min of reaction is indicated in (b) 74

Figure 36 Zeta potential distribution for as made of GO-GNP GNP and GO suspensions

as a function of the buffer solution pH 76

Figure 37 (a) Photograph of different shape CRtTR300 aerogels produced by the

developed route (b) SEM images of the cross-section perpendicular to the freezing

13

direction of CR0TR300 (c) the cross-sections perpendicular to the freezing direction

with higher magnification (d) cross-section parallel to the freezing direction (e)

SEM images of the cross-section perpendicular to the freezing direction of

CR35TR300) (f) the cross-section perpendicular to the freezing direction with

higher magnification (g) cross-section parallel to the freezing direction (Red circles

and arrows in the images indicate the freezing direction) 78

Figure 38 SEM images of (a) cross-section perpendicular to the freezing direction of

rGOTR300 (b) cross-section parallel to the freezing direction of rGOTR300 (c)

cross-section perpendicular to the freezing direction of CR60TR300 (d) cross-

section parallel to the freezing direction of CR60TR300 the cross-section

perpendicular to the freezing direction with higher magnification (g) cross-section

parallel to the freezing direction Red circles and arrows in the images indicate the

freezing direction 79

Figure 39 (a) Raman spectroscopy patterns for CRtTR300 aerogels with rGO region

(CR0TR300 CR35TR300 and CR60TR300 aerogels) and starting GO and GNP (b)

IDIG ratio (Intensity ratio of D band and G band from Raman spectroscopy) for

CRtTR300 aerogels with rGO region as a function of partial chemical reduction time

(c) XPS survey spectra were undertaken on CR0 and CRtTR300 aerogel samples

(CR0TR300 CR35TR300 and CR60TR300 aerogels) starting GO and GNP 81

Figure 310 XPS spectroscopy results for samples (a) CR0 (b) rGOTR300 samples (c)

CR35TR300 samples and (d) CR60TR300 samples 82

Figure 311 Water contact angles for rGO (rGOTR300) and rGO-GNP aerogels

(CR0TR300 CR35TR300 and CR60TR300) 83

Figure 312 (a) Compressive stress-strain curves of CRtTR300 aerogels (b) Compressive

modulus and strength of CRtTR300 aerogels for different chemical reduction times

(c) Electrical conductivities of CRtTR300 aerogels for different chemical reduction

times 84

Figure 313 The electrical conductivity of CRtTR300 (with t minutes chemical reduction

and 300 degC thermal reduction for 40 minutes at Ar atmosphere) CRtTR800 (with t

14

minutes chemical reduction and 800 oC thermal reduction for 40 minutes at Ar

atmosphere) and rGO-EEG CRtTR800 (GO with electrically exfoliated graphene at

t minutes chemical reduction and 800 oC thermal reduction for 40 minutes at Ar

atmosphere) (a) and compressive modulus of CRtTR300 samples (with t minutes

chemical reduction and 300 oC thermal reduction for 40 minutes at Ar atmosphere)

developed in this work in comparison to literature values for other nanocarbon-based

materials Reduced-graphene cellular network[161] CNT foam[162] reduced

graphene-based aerogel[99] CVD graphene foam[163] graphene elastomer[153]

3D printed graphene[164] 3D graphene macroassembly[99] 3D printing

graphene[165] GO aerogel[106] rGO-GNP hydrogel[166] and rGO

aerogel[104153167168] 85

Figure 314 The electrical conductivity of CRtTR300 samples 86

Figure 41 Schematic of aerogel composite preparation Circular images represent the

scanning electron micrograph of original samples 92

Figure 42 Morphology of aerogel composites scanning electron micrographs of (a) GA-

2 (b) GA-10 the fracture surface of (c) EGAC-2 and (d) EGC-2 95

Figure 43 Raman mapping of graphene G peak (2866 cm-1) with respect to the CH-

deformation peak of epoxy of EGAC-2 (1248 cm-1) (b) Raman spectra of epoxy

GNP and as-synthesized GO 96

Figure 44 Electrical properties of aerogel composites (a) Electrical conductivity for neat

epoxy GA-2 EGAC-2 and EGC-2 with the function of frequency (b) Electrical

conductivity of EGAC with functional of graphene loadings 97

Figure 45 Thermal properties of aerogel composites (a) DSC and (b) TGA of EGAC

with EGC and epoxy 99

Figure 46 Thermal properties of aerogel composites (a) Thermal conductivity and

thermal diffusivity of EGACs with neat epoxy 100

Figure 47 Joule heating properties of aerogel composite (a) Surface temperature versus

time showing the heating zone steady-state zone and cooling zone of aerogel

composites at an applied voltage of 5 V IR images of (b) EGAC-2 (c) EGAC-6 (d)

15

EGAC-8 and (e) EGAC-10 at steady-state zone (f) temperature line profile on spatial

variation of a thermal image of aerogel composites (g) current-voltage-power

relationship for EGAC-10 (h) steady-state temperature vs applied voltage for

EGAC-10 with fitting by quadratic equation and (i) cycle test of EGAC-10 at an

applied voltage of 5V 102

Figure 48 (a) plot of steady-state temperature with electrical conductivity of EGACs (b)

plot of steady-state temperature with thermal conductivity of EGACs (c) Radar plot

of thermal conductivity electrical conductivity and Joule heating performances of

EGAC with respect to the different GNP-content (d) Comparison plot of intrinsic

properties of EGACs with other reported aerogels The data of other aerogel are taken

from the Ref [196] 104

Figure 49 Mechanical properties of aerogel composites Flexural modulus flexural

strength and fracture toughness of neat epoxy and EGACs 105

Figure 410 Scanning electron micrograph of fracture surface for (a) neat epoxy (b-c)

EGAC-4 with different magnification and (d) EGAC-10 107

Figure 51 Schematic illustration of GOA reinforced CFEP composites preparation 113

Figure 52 (a) SEM image of GO flakes from dispersions obtained by drop-casting (b)

GO flakes width distribution (c) AFM image of GO flake from dispersion obtained

by drop-casting (d) Height profiles of the selected section labelled as 1 in Figure (c)

114

Figure 53 (a) Raman spectroscopy patterns for GO powders and rGO powders (b) XPS

spectroscopy for GO powders and rGO powders 115

Figure 54 SEM images of (a) pure CF (b) High and (c) low magnification of GOA-CF

respectively (d) Oven-dried GO-CF (Yellow arrows indicated the fiber direction and

red arrows indicated freeze direction) 116

Figure 55 Log-log plot of specific conductivity as a function of frequency for CFEP

GOA-CFEP rGOA-CFEP and oven dried GO-CFEP composites (a) in-plane

direction (b) out-of-plane direction and electrical conductivities at the frequency of

1 Hz for CFEP GOA-CFEP rGOA-CFEP and oven dried GO-CFEP composites

16

(c) in-plane direction (d) out-of-plane direction (e) Schematic description of

the x y and z directions in the specimens 118

Figure 56 Mechanical test for CFEP oven-dried GO-CFEP GOA-CFEP and rGOA-

CFEP composites (a) loading vs crack displacement (b) Normalized K1c and G1c

value by volume fraction (c) Schematic diagram of the three-point bending toughness

test 121

Figure 57 SEM images of fracture surface for (a) neat epoxy (bc) GOA-CFEP

composites (arrow indicate fracture direction) and (d) CFEP composites 123

Figure 58 Schematic diagram of the crack propagation and suppression behaviour of (a)

CFEP laminate (b) GOA-CFEP laminate (c) oven-dried GO-CFEP 124

Figure 61 Schematic of 3D epoxy resinTi3C2TX MXene aerogel composite formation

130

Figure 62 Digital images of (a) epoxy resinTi3C2TX aerogel composite (b) Ti3C2TX

aerogel before Joule heating Digital images of (c) epoxy resinTi3C2TX aerogel

composite and (d) Ti3C2TX aerogel during the Joule heating 131

Figure 63 (a) Scanning electron micrographs of fracture surface of (a) bare Ti3C2TX

aerogel and (b) epoxy resinTi3C2TX MXene aerogel composite 133

Figure 64 X-ray micro-CT of the epoxy resinTi3C2TX MXene aerogel composite

showing a cross-sectional view (left) and a 3D segmented view of a region of interest

(middle and right) showing sheets oriented within a single domain Red vectors

indicate the freezing direction The Yellow dashed box indicates a region of interest

134

Figure 65 (a) XRD patterns of delaminated Ti3C2Tx and Ti3C2Tx aerogel with its MAX

phase Plots of electrical conductivity of epoxy resinTi3C2TX aerogel composite and

Ti3C2Tx aerogel with respect to the (b) frequency and (c) temperature 136

Figure 66 X-ray photoelectron survey spectra of Ti3C2TX aerogel and epoxy resin

Ti3C2TX aerogel composite 138

Figure 67 High-resolution XPS of Ti2p C1s O1s and F1s peaks of epoxy resinTi3C2TX

MXene aerogel before Joule heating test 138

17

Figure 68 Steady-state thermal IR images of epoxy resinTi3C2TX aerogel composite held

at different input voltages of (a) 1 V (b) 125 V (c) 15V (d) 175V (e) 2V and (f) 3

V and Ti3C2TX aerogel at different voltage of (g) 1 V (h) 15 V and (i) 2 V 141

Figure 69 Temperature line profile on spatial variation of thermal image (a) epoxy

resinTi3C2TX MXene aerogel composite and (b) Ti3C2TX Mxene aerogel at an


Figure 610 Plots of (a) Temperature versus time and (b) rate of change of temperature

versus time of the epoxy resin Ti3C2TX MXene aerogel composite at different

applied voltages (c) Heating and cooling rate (solid line is guide to the eye only) and

(d) specific power of composite with respect to the applied voltage 145

Figure 611 (a) Prolonged steady-state phase and (b) Cycle test at the applied voltage of

2 V of bare MXene aerogel and epoxy resin Ti3C2TX MXene aerogel composite (c)

cycle profile of temperature for the epoxy resin Ti3C2TX MXene aerogel composite

at different applied voltages 147

Figure 612 Cycle test at an applied voltage of 2 V of (a) bare MXene aerogel and (b)

epoxy resin Ti3C2TX MXene aerogel composite 148

18

List of Abbreviations

0D Zero dimensional

1D One dimensional

2D Two dimensional

3D Three dimensional

AFM Atomic force microscopy

SEM Scanning electron microscope

CB Carbon black

CNT Carbon nanotube

GO Graphene oxide

rGO Reduced graphene oxide

GA Graphene aerogel

CFs Graphene foams

CVD Chemical vapour deposition

hBN Hexagonal boron nitride

MoS2 Molybdnum disulphide

MWCNT Multi-wall carbon nanotubes

GNP Graphene nanoplatelets

PA Polyamide

TGA Thermogravimetric analysis

XRD X-ray diffraction

XPS X-ray photoelectron spectroscopy

DMTA Dynamic mechanical thermal analysis

DSC Differential scanning calorimetry

PDMS Polydimethylsiloxane

19

List of Publications

1 Pei Yang Tian Xia Subrata Ghosh Jiacheng Wang Shelley D Rawson Philip J Withers

Ian A Kinloch Suelen Barg Realization of 3D epoxy resinTi3C2Tx MXene aerogel

composites for low-voltage electrothermal heater 2D Materials (2021) 8(2)

2 Pei Yang Gustavo Tontini Jiacheng Wang Ian A Kinloch1 and Suelen Barg Ice-

templated hybrid graphene oxide - graphene nanoplatelet lamellar architectures Tunning

mechanical and electrical properties Nanotechnology (2021) 32(20)

3 Vildan Bayram Michael Ghidiu Jae J Byun Shelley D Rawson Pei Yang Samuel A

Mcdonald Matthew Lindley Simon Fairclough Sarah J Haigh Philip J Withers Michel

W Barsoum Ian A Kinloch Suelen Barg MXene tunable lamellae architectures for

supercapacitor electrodes ACS Appl Energy Mater 2020 3 1 411ndash422

4 Pei Yang Tian Xia Zheling Li Eunice Cunha Mark Bissett Suelen Barg Ian A Kinloch

Hierarchical graphene aerogel reinforced carbon fibre composites (to be submitted)

5 Pei Yang Subrata Ghosh Tian Xia Jiacheng Wang Ian A Kinloch Suelen Barg Joule

Heating and Mechanical Properties of EpoxyGraphene-based Aerogel Composite

Influence of Graphene nanoplatelets (to be submitted)

6 Jiacheng Wang Pei Yang Subrata Ghosh Ian A Kinloch Suelen Barg Rheology and 3D

printability of aqueous graphene oxidegraphene nanoplatelets hybrid inks (to be

submitted)

20

Abstract

While polymer composites have drawn significant attention in widespread applications such as

aerospace automotive sports and thermal management Designing a novel composite with

excellent electrical thermal and mechanical properties remains a challenge The main problem

here is to construct a continuously conductive both thermally and electrically the network of

fillers for the polymer matrix which is still a subject of research Since the 2D materials with

admirable properties are anticipated as promising candidates in this context assembling

graphene-based hybrids and MXene into their 3D structure to create 2D materials aerogel-

based aerogel epoxy composites is the major focus of the present thesis

The 3D structures aerogel of 2D materials were prepared by freeze-cast method and the epoxy

was infiltrated into the aerogel followed by curing to obtain the epoxy2D materials-based

aerogel composites In the case of graphene-based composites the non-oxidized graphene

nanoplatelets (GNP) were combined with aqueous graphene oxide (GO) to improve its

electrical and mechanical properties to construct the graphene-based hybrid structure in which

epoxy was infiltrated for its Joule heating applications To explore the concept of 2D materials

aerogel reinforced polymer composites the GO aerogel was then incorporated with traditional

carbon fabrics to give hybrid composites with improved physical properties GO was prepared

by the conventional Hummers method and the reduction was done chemically and thermally to

tune the oxygen functional group and hence structural properties On the other hand other 2D

aerogel materials beyond graphene Ti3C2TX MXene 2D materials of transition metal carbide

were used as preform to create MXene aerogel-based epoxy composites for improving the

electrical conductivity and Joule heating properties

Based on the outstanding electrical thermal and mechanical properties from 2D materials-

based aerogel the epoxy was then incorporated to create multifunctional 2D materials aerogel

epoxy-based nanocomposites for Joule heating applications Moreover the mechanical

property electrical conductivity and thermal conductivity of the aerogel composites have also

been studied extensively The aerogel composites demonstrate better Joule heating

performances than the bare 2D materials aerogel The improved Joule heating performances of

aerogel composites are correlated with their electrical thermal and mechanical properties On

over that epoxy2D materials-based aerogel composites were founded to be superior as

electrothermal materials than the composite prepared by conventional shear mixing method

Finally the Joule heating performances of those epoxy2D materials-based composites are

compared between them and also with the composite reported in the literature

21

Declaration

No portion of the work referred to in the thesis has been submitted in support of an application

for another degree or qualification of this or any other university or other institutes of learning

22

Copyright

The author of this thesis (including any appendices andor schedules to this thesis) owns certain

copyright or related rights in it (the ldquoCopyrightrdquo) and she has given The University of

Manchester certain rights to use such Copyright including for administrative purposes

Copies of this thesis either in full or in extracts and whether in hard or electronic copy may

be made only in accordance with the Copyright Designs and Patents Act 1988 (as amended)

and regulations issued under it or where appropriate in accordance Presentation of Theses

Policy You are required to submit your thesis electronically 1 of 25 with licensing

agreements which the University has from time to time This page must form part of any such

copies made

The ownership of certain Copyright patents designs trademarks and other intellectual

property (the ldquoIntellectual Propertyrdquo) and any reproductions of copyright works in the thesis

for example graphs and tables (ldquoReproductionsrdquo) which may be described in this thesis may

not be owned by the author and may be owned by third parties Such Intellectual Property and

Reproductions cannot and must not be made available for use without the prior written

permission of the owner(s) of the relevant Intellectual Property andor Reproductions

Further information on the conditions under which disclosure publication and

commercialisation of this thesis the Copyright and any Intellectual Property andor

Reproductions described in it may take place is available in the University IP Policy (see

httpdocumentsmanchesteracukDocuInfoaspxDocID=24420) in any relevant Thesis

restriction declarations deposited in the University Library The University Libraryrsquos

regulations (see httpwwwlibrarymanchesteracukaboutregulations)and in The

Universityrsquos policy on Presentation of Theses

23

Acknowledgments

First I would like to appreciate my supervisors Dr Suelen Barg and Prof Ian A Kinloch for

their support and guidance during my research and their guidance is my fortune for a lifetime

I would like to thank the members of our groups ldquoAdvanced Nanomaterialsrdquo and ldquoNano 3Drdquo

who provided their support both scientifically and personally Especially I would like to thank

Dr Subrata Ghosh Tian Xia Vildan Bayram Jiacheng Wang Dr Jianyun Cao and Dr Zheling

Li for their contributions to my PhD study with fruitful discussions

I would like to send my gratitude to our collaborators at the University of Manchester Dr

Shelley D Rawson Dr Samuel A Mcdonald from Prof Philip J Witherss group Thank you

for your contributions in conducting Micro-CT characterization

Last but not least I would express my appreciation to my parents my sister and my beloved

families and friends for their love and support

24

1 Chapter 1 Introduction

11 Polymer materials

In the past decades the interest in the use of polymers as replacements for traditional materials

such as metals wood and ceramics has increased significantly[1] Polymeric materials have

many advantages such as ease to process productivity and low cost compare with conventional

materials [2] Polymeric materials are typically either thermosets or thermoplastic depending

on whether there are strong covalent crosslinks formed between the polymer chains

Thermosets are normally needed chemical reactions to form the covalent crosslinks They are

by far the predominant type of polymer in use today due to their excellent mechanical

properties chemical resistance and thermal stability They can be classified as several resin

systems such as epoxies phenolics polyurethanes and polyamides[3] and require additional

curing agents or hardeners and followed by curing steps to finish the materials Epoxy resin is

the most commonly used thermoset in the industry and hence used in this thesis An epoxy is

defined as a molecule containing more than one epoxide groups as shown in Figure 11

Figure 11 Molecular structure of epoxide group

The curing process for epoxy resin is a chemical reaction in which the epoxide groups react

with a hardenercuring agent to form a highly crosslinked three-dimensional network[4]

Depending on the chemical formulation of the curing agent the curing temperature can be

ranged from 5 to 150 degC [5] Epoxy-based materials have some limitations such as intrinsic

brittleness poor fracture toughness and electrical insulation Moreover the inelastic scattering

of polymeric chains motion restricts their effective utilization for thermal management

materials Hence epoxies need reinforcement with other materials such as fibres ceramics and

2D materials to meet the criteria for many applications in aerospace automotive electrical

25

construction medical chemical and electrothermal industries [16]

12 2D materials

The first 2D materials were experimentally observed in 2004[7] Since then the interests in

2D-related materials started blossoming due to their impressive intrinsic properties and it is

not only based on scientific interest but also for its potential technological applications

Figure 12 (a) Different kinds of the studies 2D nanomaterials[8] (b) Research development of

2D nanomaterials[9]

121 Graphene

Graphene a single layer of graphite is considered the first real two-dimensional material (one

atom thick) and was isolated in 2004 at the University of Manchester[7] Graphene can be

visualised as the basic building block of graphite and is an isotope of carbon It consists of sp2

hybridized carbon atoms in single layer formation arranged in a honeycomb structure (Figure

12)

26

Figure 13 A molecular model of a single layer of graphene[10]

The isolation of graphene has started a long time back as for early-stage researchers only

realized that the graphite consists of a host molecule or atoms with a ldquosandwichedrdquo structure

in graphite and it resulted in a weakening of interplanar forces and facilitated separation of the

layers The first single-layer graphene was prepared by the cleaving method and triggered a

tremendous effort for the materials science field in the search of other ways to produce

graphene sheets However despite the microcleavage method being simple but it shows a very

low yield of monolayers without reliability and cost-effectiveness thus this method can only

apply for academics but not for industrial

Therefore a method was needed which was more scalable and economic and could allow mass

production Thus a huge effort has been invested in solution-based techniques It started with

achievements in obtaining the suspensions of organic-molecule-coated graphene sheets using

expandable graphite[11] but the removal of the coating always leads to reaggregation of

graphene sheets to graphite After an intensive and extensive search for appropriate solvent the

colloidal suspension which contains graphene sheets was been obtained from the sonication of

graphite in organic solvents such as NMP[12] (N-methyl pyrrolidone) However this route still

had a low yield of graphene sheets

27

Graphite oxide is an alternative starting material[13] Although the exact chemical structure of

the graphite oxide surface is still resolved it is known that it consists of a layered material

composed of graphene oxide (GO) sheets where the carbon network is disrupted with a

significant amount of carbon atoms with hydroxyl groups or epoxide groups[19][20] The

presence of functional groups makes it possible to exfoliate a single layer of GO with only

stirring or mild sonication in aqueous media This method has greatly improved the yield of

single-layer graphene-like sheet production Although due to the extra-functional groups and

defects from the oxidation process both mechanical and electrical properties for GO is not as

good as graphene Compared with graphene GO is an insulator due to the disruption of its

aromaticity However it still possesses good mechanical and electrical properties from GO are

still desirable for many potential applications of graphene Restoration ordeoxygenation for

GO starts to attract peoplersquos attention to solve the extra defects from GO surfaces Removal of

functional groups from GO surfaces substantially enhances GO electrical properties by

restoring the sp2 network The reduction method for GO has made significant advances in the

past few years for improving the conductivity of GO and now these approaches can be

observed in micro-exfoliated graphene sheets[21][22]

122 MXene

MXene is the new member which joined the 2D materials family in 2011[18] It is based on

2D layered transition metal carbides nitrides or carbonitrides Like graphene MXene also

shows excellent properties due to its 2D materials nature such as large specific surface area

lightweight great mechanical properties thermal conductivity and electrical conductivities

etc However the MXene surface also contains a large number of functional groups of F O or

OH[19] Unlike graphenegraphene oxide MXene shows hydrophilic properties without losing

its excellent electrical conductivity which makes it much easier to process especially in water

for its potential applications

In general MXene is prepared from the MAX phase which consists of ternary carbides in a

layered structure with the formula Mn+1AXn the early transition metal ldquoMrdquo (Sc Ti V Cr Zr

28

Nb Mo Hf or Ta) an element from groups ldquoArdquo (Cd Al Si P S Ga Ge As In Sn Tl Pb or

S) and ldquoXrdquo is carbon andor nitrogen[20ndash24] The synthesize of MXene is always conducted

using strong acid to etching the lsquoArsquo elements between the transition metal sheets and followed

by exfoliation [20ndash22] The weaker hydrogen bonding which contents OH O or F will replace

the relatively strong metallic bonds between M and A in the formula Mn+1AXn As an example

the replacement of the A elements by using an aqueous HF as an etching agent at room

temperature is shown in Figure 13


corresponding MAX phases [25] (b) Schematic of the process of Mo2CTx synthesis by etching

the selected two Ga layers from Mo2Ga2C (purple green brown red and white represent of

Mo Ga C O and H atom respectively) (c) SEM images of MXene flakes[20]

Thus the preparation of MXenes normally involves the functionalization of hydroxyl oxygen

and fluorine groups on its surface followed by etching and exfoliation The resulting MXene

shows a significant difference to its parent MAX phase in terms of its electronic structure

MXene has been considered mostly for applications in energy conversion and storage

technologies including water splitting batteries and supercapacitors due to its excellent

physicochemical properties such as hardness high melting point high electrical and thermal

conductivity outstanding oxidation resistance hydrophilic nature and high surface area to host

a wide range of intercalants[920212326ndash31]

29

123 Other 2D material

With the discovery of graphene there is a significant trend in isolating other single-layer

materials from their bulk counterpart Boron nitrides molybdenum disulphide transition metal

dichalcogenides antennae and germanene are promising members of the 2D materials family

Boron nitride is a thermally and chemically resistant refractory compound of boron and

nitrogen with the chemical formula BN The hexagonal formed BN has a similar structure to

graphite and is therefore used as a lubricant and an additive to cosmetic products The cubic

or sphalerite structure formed by boron nitride is more like a ldquodiamondrdquo structure which is

called c-BN The rare wurtzite BN modification is like lonsdaleite but slightly softer than the

cubic form Because of the excellent thermal and chemical stability of BN it is always used in

higher temperature equipment The potential of using BN in nanotechnology has started since

it can be isolated to 2D sheets and the nanotubes of BN can be produced which followed a

similar structure with carbon nanotubes where the 2D sheets can be rolled on themselves

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur The

chemical formula is MoS2 and formed with a honeycomb structure like other 2D materials The

monolayer MoS2 can be isolated by micromechanical exfoliation or liquid-phase exfoliation

The final single layer of MoS2 shows an excellent yield strength of 270 GPa with semi-

conductive behaviour which has great potential in a wide of applications

13 Polymer nanocomposites

Compared to traditional polymer composites nanocomposites are predicted to have

extraordinary properties because of the exceptionally high surface-to-volume ratio of the

nanofiller and or its exceptionally high spec ratio[32] Polymer nanocomposites combine the

functionalities of polymeric materials with unique features of the inorganic nanoparticles such

30

as excellent toughness and strength and other properties such as electrical and thermal

conductivities[33]

131 Nanocomposites with 2D materials

Although polymer nanocomposites have shown their advantages over polymeric materials

themselves the 2D materials have boosted the development of polymer nanocomposites further

due to their high aspect ratio (lateral size varies from hundreds of nanometres to few

micrometres and their average thickness is lt5 nm) and relative ease of processing[8] Similarly

2D materials have a large surface area which facilitates good interaction with the matrix at even

very low loadings[34] For example it has been reported that with only small loading (lt1-5

wt) of 2D materials such as the layered silicates or graphene into a polymer matrix the

mechanical properties have been improved up to ~200 compared with the neat polymer[35]

So far a range of different 2D materials has been prepared and used for polymer composites

including graphene[36] graphene oxide (GO)[10] hexagonal boron nitride (h-BN)[37]

132 Epoxy2D materials based nanocomposites

The good distribution of the reinforcement of the 2D material is one of the greatest challenges

in the preparation of epoxy2D nanocomposites A well-dispersed state ensures the maximum

availability of surface area from filler and influences the properties of whole

nanocomposites[38] For epoxy the degree of dispersion of the fillers within the matrix

depends significantly on the processing technique used[39] The most commonly used method

is solution mixing where graphene is normally dispersed with epoxy resin in a suitable solvent

by bath sonication or other dispersion technique The solution mixing of polymer composites

involves the dispersion of nanofiller in the polymer solution controlled evaporation of the

solvent and finally composite casting When the epoxy and nanofiller in solution are mixed

the polymer chains are intercalated and displace the solvent which contains graphene between

the interlayer of polymer chains Once the solvent is removed the intercalated structure

31

remains and resulted in polymer nanocomposites

Solvent processing is another technique for preparing epoxy2D materials nanocomposites

This method takes advantage of the presence of functional groups attached to the graphene

surface which enables the direct dispersion of graphene in water and many organic solvents

This contributes to a strong physical or chemical interaction between the functionalized

graphene and polymeric matrices Several studies explain how the surface modification of

graphene has been done by adding various functional groups such as amine[40] organic

phosphate[41] silane[42] plasma[43] etc Functionalized graphene is normally dispersed in

a suitable solvent by different techniques such as bath sonication then mixed with epoxy resin

and followed by solvent evaporation

133 Aims and objectives

Although adding 2D material filler in epoxy resin enhances its properties and performances in

various fields[44ndash46] several drawbacks restrict the developments of 2D materialsepoxy

composites based science and technologies follow

bull the agglomeration and uneven dispersion of fillers from πndashπ stacking of 2D materials

have been found to reduce the specific surface area and active sites[47]

bull the conventional method to prepare polymer composite sometimes results in a

discontinuous filler network which limits their utilisation in the desired application It

has been reported that additional steps were adopted to make a continuous carbon

nanotube network in the polymer composite

bull Loading of fillers is another important issue Optimum loading of fillers in polymer

matrix might have enhanced electrical and thermal properties of polymer

nanocomposites however the mechanical property was found to be deteriorated

bull

Hence there is an urgent need to construct a 3D network of fillers with optimised loading and

tuneable multifunctional properties which can boost the performance of polymer composite

32

2D materials aerogel is a new class of 3D cellular interconnected material with ultra-low

density and expected to solve the problems such as agglomeration and uneven dispersion from

the fillers Aerogels of materials come with a highly porous structure with high surface area

tunable porosity and large pore volumes Aerogels normally can exhibit low density (3 Kg m-

3) high porosity (90-99 ) low thermal conductivity (0014 Wm-1 K-1 at room temperature)

low dielectric constant and low refractive index[48] So the aerogels can be applied in

electronic devices Cerenkov detectors and other fields[49] The size and shape of the

precursor nanoparticles from aerogels can control its porosity since micropores are connected

to the intra-particle structure and form macropores that connect to the inter-particle

structure[50]

Although the use of 2D materials aerogel as a scaffold to construct aerogel-based epoxy

composites allowed improvements such as mechanical properties and electrical properties for

epoxy-based polymer composites but there are still some problems and challenges to explore

the full potential reinforcement of 2D materials aerogel for epoxy composites Firstly the most

common starting materials for creating 2D materials aerogel is graphene oxide (GO) the extra

defects from GO surfaces will restrict the final properties of 2D materials aerogel epoxy

composites Although few studies have shown the reinforcement from non-oxidized graphene

it always requires special equipmentor involves toxic solvent etc Therefore a scalable and

environmentally friendly method of high-quality graphene 3D network for its polymer

composites is needed for preparing Secondly many studies exhibit great improvement for 2D

materials aerogel-based epoxy composites for their mechanical electrical and thermal

properties But this concept was only applied with neat epoxy materials Other epoxy-based

composites especially carbon fiber epoxy composites have yet been explored and studied

Thirdly among all different materials-based aerogels epoxy composites carbon-based aerogels

have been mostly studied and understood Thus another type of 2D materials such as MXene

aerogel-based epoxy composites has not been studied and explored yet

Given these considerations these has the following aims

33

1 Understand how the electrical thermal and mechanical properties of 2D-polymer

composite change when the 2D materials are connected in a continuous network as opposed to

uniformly dispersed

2 Develop a route to continuous network composites by using 2D material aerogels preforms

which are then impregnated with a polymer matrix

3 Establish if the electrical and thermal performance of GO aerogel-based composites is

improved by incorporating GNP

4 Understand if preforms are used in combination with traditional carbon fabrics to give

hybrid composites with improved physical properties

5 Show that other 2D materials beyond graphene-related materials can be used for aerogel-

based composites

6 Establish whether multifunctionality is achieved and controlled through aerogels

Following these aims the thesis has the following structure

In Chapter 1 a brief introduction of polymer materials 2D materials 2D material-epoxy

nanocomposites and 2D material aerogel-based epoxy nanocomposites are given

In Chapter 2 different techniques for preparing the aerogels with 2D materials and the

aerogels-based epoxy nanocomposites are reviewed The second part of this chapter is on the

literature review on electrical thermal mechanical and Joule heating properties Finally the

potential applications of epoxy2D materials-based aerogel composite are also reviewed

In Chapter 3 the production of GO-based hybrid graphene aerogel has been demonstrated the

additional non-oxidized graphene (GNP) was used aiming to improve the electrical

conductivity of the aerogels The process for prepared hybrid graphene aerogel involves

chemical reduction and unidirectional freeze casting Although several studies showing the

oxygen content in GO will influence the final structure of graphene aerogel the mechanism

and influence in detail are still not been fully understood especially for hybrid graphene-based

34

aerogels In this study the graphene nanoplatelets (GNP) were dispersed with GO without

additional binders or surfactants The mixture of GO and GnP first underwent chemical

reduction to tunes its oxygen content and then studied to ensure sufficient dispersibility to allow

the freeze casting technique Selected dispersions when then used to make aerogels by

unidirectional freeze casting freeze-drying and thermal reduction The final hybrid graphene

aerogels were found to possess high elastic mechanical properties and electrical properties In

addition the final aerogel showing tuneable mechanical and electrical properties with almost

unchangeable bulk densities

In Chapter 4 the hybrid graphene-based aerogel was incorporated with epoxy resin to prepare

3D graphene structure epoxy nanocomposites In this study the 3D graphene epoxy

nanocomposites were compared with graphene epoxy nanocomposites which were prepared

with a conventional shear mixing method to show the advantage of 3D graphene structure The

final 3D graphene epoxy composites showing overall improvements in terms of mechanical

properties electricalthermal conductivities and thermal stabilities compare with conventional

method prepared graphene-based epoxy nanocomposites Finally the microstructure was

investigated with 3D graphene-based epoxy nanocomposites to understand the reason for the

improvements

In chapter 5 a new method for improving carbon fibre epoxy composites is designed By

incorporating a 3D graphene structure with carbon fibre the final composites showing a

significant improvement in their electrical conductivities especially for its out-of-plane

direction as well as its toughness In this study the carbon fibre was infiltrated with GO

suspension followed by unidirectional freeze casting The solid GO aerogel CF structure

(GOA-CF) was then freeze-dried and infiltrated with epoxy resin The 3D GOA-CF structure

was investigated by scanning electron microscope After incorporated with epoxy resin several

tests were employed to investigate its mechanical and electrical properties Finally the fracture

surface was analysed to understand the reason for the overall improvements

35

In Chapter 6 a new facile approach for preparing the MXene aerogel-based epoxy composites

simply is developed The final composites showed excellent electrical conductivity of 21 Scm

Moreover the MXene aerogelepoxy composites exhibit an outstanding electrical resistance

heating profile with rapid heatingcooling performance and great repeatability This MXene

aerogelepoxy composites is anticipated as an excellent alternative to the traditional metal-

based and graphene-based electrothermal materials and could open a new opportunity for a

wide range of applications such as deicing local heater and other thermal management

applications

In Chapter 7 the main conclusions and future work are summarised

36

2 Chapter 2 Literature Review

Compared with 2D materials epoxy nanocomposites prepared with traditional methods more

advanced features can be obtained from 2D materials (mostly graphene and MXene in this

thesis) aerogel based epoxy nanocomposites such as ultra-low electrical percolation[51]

improved toughness at low fillers loading[52] outstanding thermal conductivities[53]

enhanced electrochemical performances[54] Such properties are relevant to energy

applications[55] electromagnetic shielding[56] sensor technology[57] structural

materials[58] and electrothermal heating[59] To optimize the properties of aerogel-based

polymer nanocomposites the preparation and properties of the original 2D materials aerogel

need to be considered initially Different approaches to synthesize the epoxy2D Materials

aerogel composites are then discussed Finally the intrinsic properties and their potentiality in

widespread applications are reviewed

21 Preparation of 2D materials-based aerogel

Functionalised 2D materials are the most common starting points for preparing aerogels due to

their ease of processing Chemically derived GO-based aerogels are typically used for

graphene-like aerogels[60-61] since GO possesses a lot of hydrophilic oxygen groups

including hydroxyls epoxies carbonyls and carboxyl groups and hydrophobic basal plane on

its surface[1362ndash64] Some studies showed that the processing depends on extra chemical

reagents thus it is not possible to be exploited for large-scale 2D materials-based macro-

assembly production[65ndash67] The most common and cited routes for producing the 2D

materials-based aerogels are divided into four categories (1) hydrothermal reduction method

(2) cross-linking method (3) chemical reduction method and (4) ice-templating method

211 Hydrothermal reduction method

Hydrothermal reduction is one of the most common methods for produce hydrogels from which

37

the aerogels are produced by a freeze or supercritical drying process[60][68] The hydrothermal

reduction method involves the self-assembly of GO sheets[60] requires high temperature and

high-pressure conditions and the starting solution is firmly sealed to meets the condition during

the processing[69ndash71] During the GO assembly gelationcross-linking and chemical reduction

can occur simultaneously

Xu et al [60] first reported the simple one-step assembly of rGO aerogel with the hydrothermal

method where the homogeneous GO aqueous dispersion was sealed in a Teflon-lined autoclave

and maintained at 180 degC for 1-12 hours The final hydrogel was then freeze-dried to obtain a

highly porous structure The advantage of this method are (i) it only involves a simple

hydrothermal reduction process with no multiple-step processing [127273] and (ii) it can be

used for other functionalised 2D materials to produce complex 3D structures

Figure 21 (a) Photographs of 2 mgmL GO dispersion before and after hydrothermal reduction

at 180 degC for 12 h (b) photographs of GO hydrogel allowing easy handling and supporting

weight (c-e) SEM images with low and high magnifications of rGO hydrogel microstructures

(f) room temperature I-V curve of the rGO hydrogel exhibiting Ohmic characteristic (insert for

showing a two-probe method for the conductivity measurements)[60]

38

The rGO aerogel showed a well-defined and interconnected 3D porous structure as imaged by

scanning electron microscopy (SEM) after freeze-dried samples (Figure 21 c-e) The pore size

ranged from sub-micron to several micrometers and the walls consisted of thin layers of stacked

graphene sheets The formation of physical cross-linking sites within the GO aerogel resulted

from the partial overlapping and coalescing of the flexible graphene sheets The rGO aerogel

showed an excellent apparent mechanical strength of 24 kPa and electrical conductivity of 5 times

10 -3 Scm due to the recovery of the π-conjugated system of the GO sheets during the

hydrothermal reduction as confirmed from XRD in Figure 22


aerogel[60]

The interlayer spacing of rGO aerogel was calculated to be 376 Aring which is much lower than

the GO precursor (694 Aring) and slightly higher than the natural graphite (336 Aring) The residual

hydrophilic oxygenated groups ensure that the rGO sheets can be capsulated in water during

the process of self-assembly and the π stacking results in the successful construction of the rGO

aerogels Although from this method the final graphene aerogel showed great mechanical and

electrical properties it was found that the BET surface aerogel and total pore volume of the

GA were reduced after drying as reported by Nguyen et al[74] and Li et al[75] used tri-

isocyanate for the reinforcements of GA which showed high compressibility and lightweight

and the final structure was used for crude oil absorption

39

Wu et al[76] reported an additive-free hydrothermal method to create graphene aerogels In

this method a modified solvothermal reaction of GO colloidal dispersion in ethanol was used

to create superelastic GA which can fully recover its shape even after 75 strain with near-

zero Poissonrsquos ratio in all directions The final aerogel showed repeatable compress cycles with

complete recovery over a wide temperature in air (~ 900 degC) and liquid (~ -196 degC) without

substantial degradation Moreover the temperature and frequency independent high storage

and loss modulus were obtained from the aerogel structure (Figure 23)

Figure 23 (a) Poissonrsquos ratio in the air as a function of applied strain in the axial direction (b)

Poissonrsquos ratio with a function of numbers of compression and release cycles along the axial

direction (Blue and black are Poissonrsquos ratios when the aerogel is in air and acetone

respectively) (c) The Schwartzite model for sp2-carbon phases used for the Poissonrsquos ratio

modelling[76]

A noble-metal nanocrystal-induced graphene aerogel was prepared by hydrothermal reaction

of GO suspension with noble-metal salt and glucose[77] The final self-assembled graphene

aerogel was then formed by hydrothermal treatment in the presence of divalent metal ions (Ca2+

Co2+ or Ni2+) for in-situ decoration of nanoparticles on 3D-Gs including metallic particles[78]

and alloys[79] The metal ion-induced self-assembly process was also employed for the

formation of graphene based-aerogels Ren et al [80] have developed a cost-effective

technique for the fabrication of 3D freestanding nickel nanoparticleGA using self-assembling

graphene nickel nanoparticles during the hydrothermal process[81] Wu et al reported 3D

nitrogen-doped GA-supported Fe3O4 nanoparticles by hydrothermal self-assembly This was

followed by freeze-drying and thermal treatment using polypyrrole as the nitrogen precursor

as summarized in Figure 24[82ndash84]

40

Figure 24 (a) Fabrication process for the 3D Fe3O4N-GAs catalyst stable suspension of GO

iron ions and PPy dispersed in a vial (b) Fe- and PPy-supporting graphene hybrid hydrogel

prepared by hydrothermal self-assembly and floating on water in a vial and its ideal assembled

model (c) monolithic Fe3O4N-GAs hybrid aerogel obtained after freeze-drying and thermal

treatment (de) typical SEM images of Fe3O4 N-GAs revealing the 3D macroporous structure

and uniform distribution of Fe3O4 NPs in the GAs(f) schematic diagram of the morphological

formation of highly porous Gas[82ndash84]

212 Cross-linking method

By combining the organic amine and GO at a mild temperature the nitrogen-doped graphene

aerogel has been created by the cross-linking method[85] The organic amine was used as a

nitrogen precursor and acted as a cross-linker to tune the microstructure of 3D-Gs to form the

nitrogen-doped graphene hydrogel Ultra-light fire-resistant compressible GA via self-

assembly and simultaneous reduction of GO by using ethylenediamine was reported by Li et

al[86] By following the same strategy Moon et al[87] have developed a highly elastic and

conductive N-doped monolithic GA for multifunctional applications Hexamethylenetetramine

was used as the combined reducing agent nitrogen source and graphene dispersion stabilizer

in a hydrothermal method combined with thermal treatment (Figure 25)

41


image for rGO aerogels (c) electrical conductivity of rGO aerogel with the functional of

compressive force[87]

Figure 25 (b) shows the interconnected porous network between rGO layers in each cell wall

The N-doped rGO aerogel showed an electrical conductivity of 1174 Sm at zero strain and

after a large compressive strain of 80 the electrical conductivity increased to 70423 Sm

which is the highest among all of the samples in the publication The N-doped graphene aerogel

was prepared by using the hydrothermal reduction of a GO solution with ammonia as the

nitrogen precursor for formation The resulting aerogel showed a high surface area (830 m2 g-

1) high nitrogen content (84 atom ) as well as good electrical conductivity and

wettability[88ndash90]

Besides amine layered double hydroxide (LDH) was also used as cross-linking for the self-

assembly of GO to form GAs The LDHs were found to cross-link the GO nanosheets through

hydrogen bonds and cation-π interactions[91] Lee et al [92] reported a free-standing graphene

aerogel paper with porous structure and flexible properties which was synthesized from acid-

treated glucose-strutted GAs via mechanical compression (Figure 26) Sulfur groups in the

glucose struts strengthen the GA papers owing to hydrogen bonding and thiol-carboxylic acid

esterification The hybrid aerogels exhibited high tensile strength (06 MPa) which is three

42

times higher than the GA paper without the glucose struts

Figure 26 Schematic presentation of the synthesis procedure for the glucose strutted graphene

aerogel paper[93]

213 Chemical reduction method

The chemical reduction method normally involves mild reduction agents like hydrazine

Vitamin C sodium ascorbate etc[94ndash97] to restore the sp2 network[97] as opposed to thermal

reduction via high temperature in an inert or reducing environment[71] The chemical reduction

method is considered to be superior to the hydrothermal method since the hydrothermal method

requires chemical cross-linkers high temperatures and high pressure as discussed in section

212 Chemical reduction method normally accomplished with acid[98] or base[99] as

chemical reducing agents For example Zhang et al[100] have reported the preparation of 3D

graphene aerogel from a GO solution with a reaction system of oxalic acid (OA) and sodium

iodide (NaI) The final aerogel showed low density and high porosity with great mechanical

properties It has also been found that mercapto acetic acid and mercaptoethanol can be used

as reducing agents to form 3D graphene structures since they promote in situ self-assembling

of rGO

Among all the reducing agents Vitamin C has attracted researchersrsquo attention due to its

environmentally friendly and ease of the process Zhang et al[98] has first reported the

graphene aerogel with Vitamin C via chemical reduction method and followed by freeze-dried

and supercritical CO2 dried (Figure 27) The resulting aerogels showed a low density with a

43

range from 12 to 96 mgcm3 and large Brunauer-Emmett-Teller (BET) surface areas of 512

m2g Moreover the bulk electrical conductivity of the graphene aerogel was ~1 times 102m which

is more than 2 orders of magnitude than those reported for macroscopic 3D graphene aerogels

prepared without any chemical cross-linked The morphology and porous structure were

studied by scanning electron microscopy and nitrogen sorption as can be seen in Figure 28

The uniform 3D graphene network even in a large scale of randomly oriented sheet-like

structure with wrinkled texture can be overserved and the aerogel showed a rich hierarchical

pore with a wide size distribution


mixture of graphene oxide and Vitamin C without stirring (c) The final aerogel after CO2 dried

(left) and freeze-dried (right) (d) A 71 mg graphene aerogel pillar with the diameter of 062

cm and the height of 083 cm supporting 100 g counterpoise more than 14000 times its own

weight[98]

The mechanical properties of aerogel have been investigated by compression test with a loading

speed of 2 mmmin which shows two regions during the compression test an elastic region and

a yield region In the elastic region the solid walls of various pores in the graphene aerogels

have experienced elastic bending while the graphene aerogel pores start to collapse gradually

in the yield region when then stress slowly increased Youngrsquos modulus was 12-62 Mpa in the

elastic region and 03-22 Mpa in the yield region Finally due to the large specific area of the

44

graphene aerogel the aerogels were tested for their potential supercapacitors in a 6 molL KOH

electrolyte The CV curve of the graphene aerogel with a density of 46 mgcm3 at a scan rate

of 2 mVS showed a typical rectangular shape as shown in Figure 29 And its specific

capacitance of 128 Fg (at a constant current of 50 mAg) has been obtained which ensures the

great potential for its supercapacitors in a wide range of applications By following the same

process Vitamin C reduction method Tang et al[101] have developed a graphene aerogel with

excellent mechanical properties and demonstrated full recovery after being compressed by

strain up to 80 and 47 kPa Youngrsquos modulus with only 12 mgcm3 density

Figure 28 SEM images of supercritical CO2 dried (a) and freeze-dried (b) graphene aerogels

and typical nitrogen sorption isotherms (c) BJH (BarretndashJoynerndashHalenda) desorption pore size

distribution (d) of these graphene aerogels[85]

214 Ice-template method

The ice-template method or freeze casting method is a well-known wet shaping technique for

forming porous materials It involves a complicated freezing dynamic Serval studies showed

that not only the properties of final aerogel were influenced by freeze speed but it also can be

influenced by the solution used the pattern of the freezing surface the dimension of particlesor

45

flakes the size of freezing moulds etc[102] However solidification and crystallization are

always at the very heart of making porous materials The first fabrication of GAs by freeze

casting was reported by Vickery et al[65] in 2009 Followed by the same concept Xie et al

[103] have reported GAs that can be tailored with large-range porous architecture and its

mechanical properties By changing the freezing speed by adjusting the final freeze-cast

temperature (Figure 29) it has been shown that the pore sizes and wall thickness of aerogel

can be gradually tuned from 105 to 800 microm and 20 nm to 80 microm respectively Also the wetting

property was changed from hydrophilic to hydrophobic and Youngrsquos modulus was varied by

15 times

Figure 29 (a) Qualitative schematic of the relationship between nucleation and crystal growth

as a function of freezing temperature during ice solidification (b) Performance of water

absorptionresistance on the cross-section of a sponge[103]

Na et al [104] reported that the final aerogel with a bigger size of rGO flakes (gt20 μm) was

superelastic exhibited high energy absorption and much enhanced mechanical properties than

those with small flakes (lt 2 μm) Besides this the differences in microstructure such as pore

size and wall distance were also observed (Figure 210)

46


direction) of a GO-PN fabricated by freeze casting of GO-sus (c) Foam-like porous networks

fabricated by using high concentrated oil-in-water emulsions (75 vol ) and (d) hybrid foam-

lamellar structure fabricated through the freeze casting of oil in water emulsions with low oil

content (25 vol ) (e) A lamellar GO-PN produced from GO-sus of the same density (5thinspmgml)

as those used for samples shown in (ab) but using smaller GO flakes (lt2thinspμm) than (ab) (20ndash

60thinspμm) (f) An rGO-PN network after the heat treatment at 1223K[105]

During the freeze casting the ice crystals nucleation and growth ejected the GO flakes from

the moving ice front rearranged the flakes between ice crystals and finally formed a

continuous network (Figure 210) The lower freezing front speed can lead to large scale cells

of the GO network the final aerogel showed a 466thinspplusmnthinsp183thinspμm pore with 1 K min-1 and 138thinspplusmn

47

thinsp34thinspμm once the freeze front speed has increased to 10 K min-1 For mechanical properties the

bigger flakes rGO aerogel showed relatively higher compressive strength and Youngrsquos modulus

Moreover the study has shown that higher thermal reduction temperature can result the

aerogels with better strength recovery due to the fewer defects from the rGO Wang et al[106]

reported a freeze casting technique with a local structure that mimics turbine blades The

centimeter-scale radiating structure with many channels was achieved by controlling the

formation of the ice crystals in the aqueous GO dispersion that grew radially in the shape of

lamellae during freezing (Figure 211)


freezing (a) Scheme of the fabrication process (b) The freezing set up for making the radiating

structure has a copper rod with its upper surface hollowed out (c) Two temperature gradients

are induced by the upper copper mold (d) Model of the ice crystals growing along with radial

directions because of the two temperature gradients The orange sheets represent the dispersed

graphene oxide sheets[106]

As shown in Figure 212 the GO sheets were lamellar and ordered along with radial directions

in a centrosymmetric pattern which indicates a large and lamellar shape of ice crystals During

the freezing lamellar ice crystals have grown preferentially from the edge to the center of the

copper mold As the ice front is curved the spacing between the lamellae becomes narrower

48

the closer to the center of the mould (Figure 212 c) For a typical GO aerogel sample made by

this bidirectional freezing mold the channel width was increased from about 918 μm (Figure

212 d near the center) to about 270 μm and about 4017 μm (Figure 212 f near the edge)

The thickness of these channel walls was increased from about 68 nm to about 101 and 177

nm

Figure 212 Optical and SEM images of GO aerogels made by adding different additives and

comparison of BDF with conventional freezing methods (a) Ultralow density (69 mg cmminus3 )

rGO aerogel made by adding ethanol during freezing standing on grass (b) rGO aerogel with

a weight of 27 mg can sustain 290 g of iron blocks (c) rGOcellulose nanofiber (CeNF)

nanocomposite aerogel with an obvious radiating pattern on its surface (d) GOchitosan

aerogel without chemical reduction one can also see the texture on the surface (e) SEM image

of the rG-OCeNF nanocomposite aerogel (fg) SEM images of GOchitosan aerogels even a

spiral pattern can be obtained (hminusj) Illustrations comparing BDF and conventional freezing

methods using three cylindrical molds projected to the plane of the paper[106]

The final rGO aerogel with bidirectional freeze casting method showed an excellent recovery

even after 1000 compressive cycles with only 8 permanent deformation Moreover the

49

aerogel sample can float on water rapidly with great oil fouling in just a few seconds The

maximum adsorption capacity was 3747 g g-1 which is a much higher value compared with

the normal freeze casting technique The aerogel with changing widths of aligned channels

makes it a potentially superior configuration to perform as an adsorbent such as for treating

contaminated water

The freeze casting technique can be also applied to MXene aerogel preparation Vildan et al

[107] has recently reported a method to prepare MXene aerogel via freeze casting technique

The Ti3AlC2 powder was firstly etched with LiF and HCl to create MXene solution and then

followed by unidirectional freeze-casting After freeze-drying the MXene aerogel (MA) was

prepared with different density ranges from 7-43 mgcm3 The aerogel was then compressed

and rolled for preparing MXene electrodes The final MXene based electrodes could potentially

overcome some limitations such as introducing other 2D materials as spacers between MXene

flakes to avoid their restacking separating MXene layers with surfactants creating porous

structures via additional chemical and thermal processes in parallel with vacuum filtrations

and creating 3D crumpled MXene structures via spray drying and other approaches

50

Figure 213 Schematics and images of the fabrication strategy to produce Ti3C2Tx aerogels

and supercapacitor electrodes by using three different approaches From the top left of the

image following the arrows optical photographs and SEM images of Ti3AlC2 particles the

image of the mold on top of the freeze caster containing the Ti3C2Tx suspension (aqueous

suspensions is schematically illustrated) and corresponding SEM image of a few layers sheet

unidirectional freeze-cast sample inside the mold (schematic of the microstructure formation

during ice crystal growth) optical photographs and SEM images of electrode layers in the form

of as-prepared MA (lamellae architecture formed within the aerogel is schematically

illustrated) pressed (P-MA) and rolled Ti3C2Tx aerogel (R-MA) The range of electrode

densities (ρ) achieved by each approach is also indicated The red vectors inserted in the SEM

images indicate the freezing direction[107]

Bian et al[108] has reported ultralight MXene-based aerogels prepared with freeze-casting

technique with high electromagnetic interference shielding performance The final aerogel

only has a density of less than 10 mgcm3 and gave an excellent EMI shielding performance

(up to 75 dB) with extremely low reflection (lt1 dB) which was equals to 9904 dBcm3g with

its specific shielding effectiveness Moreover MXene aerogel can be used in other applications

Zhang et al[109] have demonstrated the MXene based aerogel has great potential for solar

51

desalination with high efficiency and salt resistance The final aerogel prepared with freeze

casting technique exhibited a high conversion efficiency (87) and stable water yield for 15

days (~146 kgm2h) under 1 sun About 6 Lm2 of freshwater was output daily from seawater

22 Preparation of 2D materials aerogel-based polymer nanocomposites

Keeping 2D materials-based aerogel structure as scaffolds polymer composites were prepared

by various strategies The fabrication methods for 2D materials aerogel-based polymer

nanocomposites were found to be influential to define the structure-behavior of composites

The different types of fabrication techniques include dip coating casting electrostatic spray

deposition and vacuum infiltration method

221 Dip coating

The dip coating method can be applied for producing liquid polymeric matrix materials

composites This method typically involves the immersion of aerogels in the polymer solution

and by varying the parameters one can tune both the quality and formation of the coating and

composites For example the dipping time and 2D materials content are deciding factors for

determining the thickness of the coating After the completion of dip coating the mixture of

2D materials aerogel and polymer solution were cured under specific time and temperature

conditions Figure 214 shows a schematic of the dip coating process for graphene aerogel in

the polymer Figure 214 (a and b) represent the gradual dipping and holding of graphene

aerogel in the liquid polymer using a control apparatus respectively In Figure 214(c) after

the immersion of graphene aerogel-polymer it was removed from the precursor The whole

system was then cured by using UV light or heat source in Figure 214(d)

52


composites[110]

222 Casting approach

Casting is another processing method for complete infiltration of 2D materials aerogel with the

polymer solution It involves pouring polymer into a mold containing 2D materials aerogel In

this case the polymer solution needs to be low viscous to infiltrates through the pore and coats

of aerogel Once the infiltration complete the whole system will be cured under specific

conditions[111]

223 Electrostatic spray deposition

The electrostatic spray deposition technique can be also adopted to fabricate aerogel-based

composites This method used the spraying technique to deposit polymer matrix in the powder

form on the 2D materials aerogel to create aerogel-based polymer composites Figure 215

explains the electrostatic spray coating deposition process Once 2D materials aerogel connects

to an electrically conductive metal foil the spray gun applies an electrostatic charge to the

polymer powder particles that attract to the aerogel structure The specified thickness of

polymer deposition from the aerogel structure can be controlled by spray time and spray

distance After curing the polymer formed a continuous thin layer on the aerogel structure if it

has good wetting behavior with the aerogel structure At last curing all these components under

53

specific conditions formed the aerogel-based polymer composites

Figure 215 Schematic of the electrostatic spray coating process[111]

224 Vacuum infiltration technique

The vacuum infiltration approach is the most commonly used method to prepare aerogel-based

polymer composites In this method polymeric materials are infiltrated through the macro-

porous architecture of 2D materials aerogel under vacuum to make sure the full infiltration

After the infiltration the whole system is cured at specific conditions and creates aerogel-based

polymer composites

Figure 216 The processing of vacuum infiltration technique (UGA Unidirectional graphene

aerogel)[52]

54

23 Properties of 2D aerogel-based polymer composites

231 Electrical properties

The synergy of polymer and 2D materials aerogel as nano-reinforcement has exhibited

impressive electrical properties of 2D materials aerogel-based polymer composites For 2D

materials reinforced polymer nanocomposites prepared by a conventional method it normally

needs a large amount of 2D materials fillers to form the electrical percolation However due to

the 3D porous structure from aerogel-based polymer composites the percolation can be formed

at ultra-low loading For example Wang et al[51] managed to get the graphene aerogelepoxy

composites conductive with only 0007 vol Furthermore by increasing the loading of

graphene by only 001 vol a remarkable ~8 orders of magnitude increase in electrical

conductivity has been demonstrated The highest electrical conductivity in their study has been

achieved at 12 Sm at a graphene content of 016 vol which could be sufficient for many

practical applications


concentration (b) DC electrical conductivities of GAepoxy composites in the alignment

direction and transverse to it [112]

It has been considered that the size of fillers also influenced the electrical conductivity of

aerogel-based polymer composites Han et al[112] demonstrated that the composites with a

large size of graphene flakes have more well-formed percolation and conductive network

Ultra-large GA (UGA) formed from the ultra-large-GO (UL-GO) sheets exhibited an electrical

55

conductivity of 0178 Scm along the alignment direction whereas the corresponding

UGAepoxy composites have an electrical conductivity of 0135 Scm at 011 vol of UL-

UGA (Figure 219) Compared with each corresponding pair data the conductivities of

UGAepoxy were only slightly lower than those of the respective UGA reinforcements because

of damaged 3D interconnected graphene network causes by the pressure experienced during

the vacuum infiltration method

Apart from flakes size influence the quality of 2D materials also influenced the electrical

properties of aerogel-based polymer composites Kim et al[113] reported the fabrication of

highly crystalline GA using large nonoxidized graphene flakes (NOGFs) and infiltrated with

epoxy resin to create nonoxidized graphene aerogel (NOGA) epoxy composites The electrical

conductivity of NOGA-epoxy composites displayed an increasing trend with rising NOGF

content An excellent electrical conductivity of 1226 Sm was achieved at 027 vol of NOGF

loading in the direction parallel to the alignment at NOFG content which is approximately 12

orders of magnitude higher than that of neat epoxy (Figure 220) They believed such dramatic

enhancement of electrical conductivity is because of the high-quality nonoxidized graphene

flakes and the 3D aerogel structure Not only the graphene quality and the loading of the fillers

will influence the electrical conductivity of graphene aerogel-based epoxy composites but the

test directions The electrical conductivity in parallel direction showing several times higher

than its transverse direction and this phenomenon have been reported by most studies in this

section this is due to the isotropic graphene aerogel network nature Moreover the

disconnections of the graphene network align the transverse direction reduced the density of

electrical paths thus decrease the electrical conductivity of samples

56

Figure 218 The electrical conductivity of NOGA-epoxy composites in orthogonal directions

at different NOGF content[113]

232 Thermal properties

Figure 219 Scheme of thermal and electron transport in composites reinforced with 1D 2D

57

and 3D graphene foam[110]

Pettes et al [114] first observed an increase in thermal conductivity of free-standing graphene

aerogel from 026 to 17 Wm-1K-1 by using different etchants for nickel foam Moreover the

pure graphene aerogel showed an improved thermal conductivity as the temperature increased

above room temperature[115] Graphene aerogel also has a low thermal interfacial resistance

of 004 cm2KW-1 which is ten times lower than the conventional thermal paste and grease used

as thermal interface materials[116] With all these unique thermal properties the combination

of 2D materials aerogel and polymer have great potential in the improvement of thermal

properties for its composites For example graphene aerogel-basedPDMS composites have a

very low thermal resistance of 14 mm2 KW-1[117] owing to the interconnected structure of

graphene aerogel The thermal behavior of polyimide and polyamide matrix aerogel

composites has also been studied The thermal conductivity of neat polyimide (02 W m-1K-1)

has been significantly improved to 185 W m-1K-1 with an additional 01 wt of graphene

aerogels at 150 degC (Figure 221) suggesting that the 3D interconnected structure of graphene

aerogel increased the phonon flow with the PI graphene aerogel composites The comparison

of PDMS graphene aerogel composites and PI graphene aerogel composites indicated that PI-

based composites possessed higher thermal conductivity and stability than PDMS-based

composites which could be due to smaller interface area exposure of PI graphene aerogel to

air unlike PDMS

58


PDMS and 07 wt graphene aerogelPDMS at 85 degC[110]

Similar to the electrical conductivity behavior of aerogel-based polymer composites the

thermal conductivity of the composites also showed an increasing trend as the loading

increased[110] Figure 222 presents the thermal conductivity behavior of polymer composites

with varying content of the graphene foam and flakes fillers An almost linear increase of

thermal conductivity with the function of filler content was observed Moreover

polyamidegraphene aerogel revealed better thermal conductivity than the multi-graphene

flakes in PDMS[118] portraying that the hierarchical structure of graphene aerogel is

conductive for thermal conduction

59



Yao et al [119] reported an rGO-BN aerogel-based epoxy composite which exhibited an

excellent thermal property In their study the hybrid aerogel was produced by the freeze casting

method followed by epoxy infiltration to create BN-rGO epoxy composites The neat epoxy

has a low thermal conductivity of 018 W m-1K-1 at room temperature The existence of a 3D

BN-rGO structure resulted in a dramatic enhancement of the thermal conductivity of the epoxy

resin The maximum thermal conductivity of 505 W m-1K-1 in BN-rGOepoxy composites was

achieved with 1316 vol BN-rGO at room temperature which is 27 times higher than that of

the neat epoxy resin (Figure 223) As a comparison the same loading of raw BN-rGO epoxy

composites thermal conductivity has been measured but only achieved half value of 3D BN-

rGO epoxy composites indicated the benefit from fillerrsquos 3D structure

60



233 Joule heating properties

The aerogel-based polymer composites are expected to have excellent Joule heating properties

because of their outstanding electrical and thermal properties Bustillos et al [120] first

demonstrated the Joule heating performance of graphene foam-based PDMS composites (GrF-

PDMS) The graphene foam was first formed by the CVD technique and the PDMS then

infiltrated under vacuum The composites showed a rapid heating rate of 087 degCs a steady-

state temperature of ~70 degC with only 1 W power input (Figure 224)

61

Figure 223 (a) Heating profiles of GrFminusPDMS composite as a function of increasing currents

(at room temperature 25 degC) (b) Heating profile of the 01 vol GrFminusPDMS composite at

room temperature and input current of 04 A (c) Schematic representation of restricted phonon

transport is poorly dispersed conductive filler composites vs uninterrupted phonon transport in

GrF[120]

Moreover the composites have been tested with 100 cycles and showed an almost

unchangeable steady-state surface temperature Ju et al[109] reported 3D MXene structure-

based composites with their Joule heating properties (Figure 225) The composites reach

402 degC in 10 mins Compared with the MXene membrane the 3D MXene aerogel-based

composites showed a higher steady-state surface temperature and higher heating rate

The Joule heating properties of 2D materials-aerogel based composites showing the same trend

as its electrical and thermal properties several studies reported with the increasing the fillers

loading in the composites system the samples showing better Joule heating properties such as

higher steady-state temperature quicker response time higher heating rate etc[120]

62


234 Mechanical properties

Significant mechanical properties enhancement of 2D materials aerogel-based polymer

composites have been reported and reviewed below Examples of polymer here discussed here

including Polydimethylsiloxane (PDMS)[120ndash123] epoxy[111][124][125] and

polyimide[126]

Wang et al [52] prepared graphene aerogel-based epoxy composites by infiltrating epoxy resin

into chemical reduced graphene aerogels They have managed to increase the flexural modulus

in the alignment direction by about 12 with 05 wt graphene as well as flexural strength

However once the loading passes a certain point (05 wt) both flexural modulus and strength

did not show any increase further Along the transverse direction the initial trend was found to

be the same as the alignment direction until loading reaches 05 wt After the loading over

05 wt both flexural modulus and strength start to decrease Kim et al [113] found that the

flexural modulus was enhanced by 254 and the flexural strength by 102 at a low loading

of 034 vol compared with the neat epoxy Moreover the fracture toughness on the other

hand exhibited a sharp enhancement The composites delivered an excellent mechanical

property with a maximum increase of 761 in K1c at 045 vol (Figure 226)

63


strength and (b) fracture toughness of GA-epoxy composites as a function of graphene

content[113]

Han et al[112] demonstrated the influence of fillerrsquos dimension for aerogel-based epoxy

composites In their study graphene aerogel has been assembled by using both ultra-large GO

flakes (UL-UGA) and small GO flakes (S-UGA) and infiltrated with epoxy resin The results

showed that the composites based on ultra-large GO flakes have higher flexural strength and

fracture toughness compared to that of small GO flakes Besides this they have discussed the

mechanism for mechanical properties enhancement (Figure 227) It is believed that all

graphene-based aerogel epoxy composites showing remarkable improvements in fracture

resistance at low filler loading were due to the excellent properties from graphene aerogels

originating from the highly preserved crystallinity and graphitic structure Also the fracture

toughens is expected to be enhanced significantly due to effective crack propagation hindrance

by the horizontally aligned graphene walls from graphene aerogel However at the certain

loading point of graphene there is no further improvement in terms of its flexural modulus

flexural strength and fracture toughness This might because of the slight graphene aggeration

that happens at higher loading thus decrease the mechanical properties of the composites

system

64

Figure 226 Typical SEM images of fracture surface for (a) neat epoxy and epoxy composites

with (b) 004 vol (c) 011 vol and (d) 022 vol UL-UGA aligned against the crack

plane (e) fracture toughness of UL-UGA and S-UGAepoxy composites SEM image of

fracture surface of S-UGA composite with (f) 016 vol (g) 004 vol (h) 007 vol and

(i) 011 vol of UL-UGA[112]

235 Other properties

2D materials aerogel-based polymer composites also exhibited other excellent properties

including biological acoustic and chemical For example Nieto et al[127] studied bio-tolerant

and biocompatibility properties of graphene aerogel-based composites in the culturing of

human mesenchymal stem cells (hMSCs) Cellular studies showed that the hMSCs survived

and proliferated on the 3D graphene aerogel reinforced composite In another study

polydopamine PDAgraphene aerogel composites were produced for enzyme

immobilization[128]

A recent study showed that the graphene aerogeltungstenepoxy composites produced an

improved acoustic performance[125] The hierarchical and mesoporous structure was

65

employed in the epoxy matrix and thus provides a confined space that allows a dense packing

of the tungsten spheres within the pores of aerogel The compactness among epoxy tungsten

spheres and graphene aerogel would result in a reduction of air that can propagate acoustic

waves This would thereby lead to high acoustic impedance and increased acoustic attenuation

which is required for excellent backing material

24 Potential application of 2D materials aerogel-based polymer composites

Due to the excellent electrical mechanical thermal and Joule heating properties of 2D

materials aerogel-based polymer composites as discussed above it is expected to open the

avenues where the polymer composites can be used in a wide range of engineering applications

The 2D materials aerogel-based polymer composites can be used in electronic devices flexible

electronics strain sensors electromagnetic interference (EMI) shielding and electrochemical

biosensors in the electronic industry

For EMI shielding materials it requires materials that can prevent the detrimental effects of

EMI interference and microwave on humans and electronics The graphene aerogel-based

PDMS composites can produce a specific EMI shielding that can be up to 500 dB cm3g[129]

Also the graphene aerogel-based polymer composites can provide high-performance

supercapacitors with improved cyclic stability of up to 6000 cycles[130] Besides aerogel-

based polymer composites provide sufficient capacity to be used as thermal interface materials

for chips low thermal resistance and high thermal conductivity[118120131] Combing both

excellent electrical and thermal properties from the 2D aerogel based polymer composites the

rapid heating and high Joule heating efficiency from its nature they can be used as a local

heater deicing devices and other electrothermal devices in the aerospace automotive and

sports industry[132133] Table 2-

1 summarised the 2D aerogel-based polymer composites with different materials properties for

various engineering applications

66


composites

Material

Property

Composites Applications

Electrical

properties

GrapheneMXene aerogel-

PDMSepoxyPolypyrrole

PANI sponge

Supercapacitors adsorbent strain

sensor electrochemical biosensor

space vehicle protection

Mechanical

properties


PDMSepoxy

Dampers packaging strain sensors

Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide

Thermal interface materials high

power electronics flame-resistant

material

25 Conclusion

Various strategies to synthesize the 2D materials based on aerogel and composites with polymer

are briefed Progress of polymer2D materials aerogel-based composites in terms of intrinsic

properties and their potential applications are also discussed The potential applications of the

polymer2D materials-based aerogel composite are also addressed

67

3 Chapter 3 Ice-templated hybrid graphene oxide -

graphene nanoplatelet lamellar architectures with

tunable mechanical and electrical properties

This Chapter emphasises the design of 3D graphene-based architecture using the stable

suspension of GO and GNP Here a versatile aqueous processing route is presented to produce

lamellar aerogels structure of GO-GNP composites via unidirectional freeze-casting To

optimise the properties of the aerogel GO-GNP dispersions were partially reduced by L-

ascorbic acid prior to freeze-casting for tuning the carbon and oxygen (CO) ratio The aerogels

were heat treated afterward to fully reduce the GO Morphology and structure of reduced

graphene oxide(rGO)GNP aerogel was investigated by scanning electron micrograph Raman

spectroscopy and X-Ray diffraction The properties of the final aerogels were characterized by

electrical conductivity test mechanical test and water contact angle test An optimal partial

reduction time of 35 mins led to an aerogel with the compressive modulus of 051 plusmn 006 Mpa

at a density of 232 plusmn 07 mgcm3 and an electrical conductivity of 423 Sm at a density of

208 plusmn 08 mgcm3 was achieved with partial reduction of 60 mins

31 Introduction

Generally GO is the preferred precursor to produce such aerogels due to the aqueous

preparation routes used as discussed in Chapter 2[60134] And among all producing methods

freeze-casting is one of the most popular for obtaining porous 3D structure because it allows

the formation of an anisotropic microstructure with controllable and uniform macropores[135]

Consequently despite freeze-casting of GO water suspension being a convenient and scalable

method extra defects are generally introduced to the materials surface both during processing

and post-reduction-treatment and severely hinder the properties of interest On the other hand

non-functionalised graphene-based materials such as pristine graphene and graphene

nanoplatelets (GNP) cannot easily be stabilised in suspensions due to their poor dispersibility

68

in both aqueous and organic solvents Several approaches have been studied for the production

of the stable aqueous suspension of graphene[136ndash138] Chemical functionalisation of

graphene with highly concentrated acid is a widely used technique to increase their

dispersibility[139140] However the modification via chemical route can disrupt the

electronic paths in graphene and deteriorate the electrical and other quantum effect properties

of the structures[140] To address this issue some studies have adopted a non-covalent

approach by using surfactant as well as charged and uncharged polymers for dispersing

graphene materials with homogenization and ultrasonication[141142] though the stabilizing

effect is still limited Recently Kazi et al[143] has reported that GNP can be dispersed in GO

water suspension with a wide range of pH values Thus it would be very useful to combine

this approach with freeze casting to create high-quality graphene-based aerogel

In this work a binder-free freeze-cast graphene-based aerogel with tunable CO ratio (Figure

31) has been developed which is based on the use of GO as a multi-purpose colloid that enables

the aqueous dispersion of GNP at concentrations as high as 80 wt (at 41 GNP GO ratios)

aids in the formation of the 3D network and can subsequently restore its π-π conjugated

structure of graphene after partially chemical reduction and contribute to the final aerogel

properties The resulting suspension was later processed by unidirectional freeze-casting

freeze-drying and thermal reduction to obtain a light-weight 3D structure Initially the

dispersions and role of the chemical reduction time on the oxygen contents of the aerogels were

studied and analysed via Raman spectroscopy and X-ray photoelectron spectroscopy The GO-

GNP suspension stability was characterized via zeta potential before and after the partial

chemical reduction process

69

Figure 31 Schematic of the processing route towards rGO-GNP lamellar aerogels (First row

schematic of processing route for rGO-GNP lamellar aerogels Second row Details of

processing from frozen structure to rGO-GNP lamellar aerogel) From left to right GNP is

incorporated into GO aqueous suspensions via shear mixing the GO-GNP suspensions are

partially reduced with L-ascorbic acid at 50 degC for different times t these are subsequently

freeze casted and dried to form lamellae structures templated by the ice crystals after a freeze-

drying step the aerogels are subjected to a final thermal treatment at 300 and 800 degC in Ar

32 Materials and methods

321 Materials

The reagents used were L-ascorbic acid (Sigma-Aldrich L-ascorbic acid 99) graphite flakes

(grade 2369 Graphexel Ltd UK) sodium nitrate (Sigma-Aldrich ACS reagent ge990)

potassium permanganate (KMnO4 Sigma-Aldrich ACS reagent ge990) sulfuric acid

(ACROS Organics 96 solution in water extra pure) and hydrogen peroxide (H2O2 Scientific

Laboratory Supplies 35 solution in water 100 volumes) The graphene nanoplatelets (GNP

M-25 XGscience USA) had a flake size of 107 plusmn 37 microm(Figure 31) and a thickness of ~45

nm (Figure 32)

322 Synthesis of Graphene Oxide

GO flakes were produced using a modified Hummersrsquo method[144] Firstly 38 g of sodium

nitrate was dissolved in 169 mL of sulfuric acid and stirred constantly for 10 minutes in the ice

70

bath 5 g of graphite flakes were then added and stirred for a further 10 minutes Finally 225

g of KMnO4 was gradually added to the mixture over 30 minutes The mixture was allowed to

warm to room temperature and then continuously stirred for 4 days to consume the KMnO4 as

evidenced by the diminished green colour After the first day 152 mL sulfuric was added every

24 hours for the remaining 3 days After 4 days the viscous oxidized mixture was slowly

dispersed in a solution of water (9834 mL) H2O2 (8 mL) and sulfuric acid (9 mL) in an ice

bath The mixture became light-yellow and was continuously stirred for 2 hours after the initial

effervescence stopped The product was centrifuged at 8000 rpm for 30 minutes to separate the

produced GO from the acid solution The GO precipitate was repeatedly washed and

centrifuged with the acidic solution (9834 mL of water 8 mL of H2O2 and 9 mL of sulfuric

acid) 7 times and subsequently washed with deionised water until the pH of the supernatant

was about 5 (after 15 washing cycles) The resulting dark brown-orange viscous GO sol (~10

mg mLminus1) was diluted down to 5 mg mLminus1 using deionised water for further application The

resulting GO had a flake size of 78 plusmn 31 um (Figure 32) and thickness of ~26 nm (Figure

33)

Figure 32 SEM images of (a) graphene oxide (GO) flakes and (c) graphene nanoplatelet (GNP)

flakes (both with flakes width distribution)

71

Figure 33 AFM images of (a) graphene oxide (GO) flakes and (b) graphene nanoplatelet (GNP)

flakes

323 Production of the rGO-GNP Aerogels

GNP powder was added to 10 mL of the GO suspension (5 mg mL-1) at GNP GO weight ratios

of 41 and homogenised in the ice bath (IKA T25 digital Ultra Turrax) at 15000 rpm for 20

minutes A black-coloured aqueous suspension with a solid concentration of 25 mg mL-1 GO-

GNP was formed 50 mg of L-ascorbic acid was then added to the suspension (11 mass ratio

of GO to L-ascorbic acid) homogenised by shear mixing for 10 minutes in the ice bath and

then placed into a water bath at 50 degC for a given time t minutes Samples were prepared with

t from 0 to 60 minutes at 5 minutes steps to investigate the partial reduction treatment Then

the partially chemically reduced GO-GNP (denoted as CRt) suspension was frozen by

unidirectional freeze-casting using a lab-built freeze caster as described in our previous

work[145] and a PTFE cylindrical mould (20 mm diameter and 20 mm height) Freeze-casting

was conducted from 20 degC to -100 degC at a cooling rate of 5 degCmin The frozen samples were

freeze-dried to yields aerogels These have made CRt aerogels did not show any significant

electrical conductivity so they were thermally treated at either 300 or 800 degC in an argon

72

atmosphere for 40 minutes

The resulting samples were labelled as CRtTR300 and CRtTR800 where ldquotrdquo is the partial

chemical reduction (CR) time (minutes) TR300 and TR800 stand for thermal reduction (TR)

at 300 degC and 800 degC respectively

324 Zeta potential characterisation

The zeta potential of the particles in the GO-GNP suspensions was investigated by a Zetasizer

Nano ZS (Malvern Instruments Ltd Malvern UK) using 4 mW He-Ne laser operating at a

wavelength of 633 nm with detection angle of 13deg the pH of the suspension was adjusted by

001 molL NaOH buffer solution for higher pH and 001 molL HCl buffer solution for lower

pH

325 Morphylogy and microstructure

Raman specra were collected from the aerogels using a Renishaw System 1000 Raman

Spectrometer with a 514 nm excitation laser WIRE 32 software was used to deconvolute the

Raman spectra of the as-received GNP as-synthesized GO and rGO-GNP aerogels X-

ray photoelectron spectra (XPS) measurements were performed by a PHI Quantera SXMAES

650 Auger Electron Spectrometer (ULVAC-PHI Inc) equipped with a hemispherical electron

analyzer and a scanning monochromated Al Kα (hυ = 14866 eV) X-ray source

The microstructure of the aerogels was further investigated by using scanning electron

microscopy (FEI Quanta 250) For the morphylogy of GO and GNP powders the sample

preparation for SEM and AFM samples are both the same firstly a very dilute GOwater

solution was made by bath sonicate for 10 mins Then the solution was drop cast on a SiO2Si

wafer and dried overnight under room temperature Finally the sample was mounted to an

aluminium SEM stub by carbon tapeThe density of the samples was determined by measuring

their dimensions using a digital Vernier caliper and their mass using a balance with 0001 mg

accuracy

73


The mechanical properties of the aerogels were measured by Instron 3344L3927 in

compression mode with a load speed of 05 mms and unload speed of 005 mms due to the

slow recovery rate

The electrical was measured by NumetriQ PSM1735 analyzer where the samples were coated

with silver paint on both sides in order to reduce the contact resistance with Impedance Analysis

Interface whose frequency (ω) ranges from 1 to 106 Hz The specific conductivities (σ) of the

samples were calculated by the equation

120590(120596) = |119884lowast(120596)|119905

119860 =

1

119885lowast times 119905

119860 (31)

where Y(ω) is the complex admittance Z is the complex impedance t is the thickness

and A is the cross-sectional area of the sample




slow recovery rate

33 Results and Discussion

331 Rheology of suspension as a function of chemical reduction time

74

Figure 34 Digital images of GO-GNP suspensions as-prepared CR0 (a) after 35 min CR35

(b) and after 60 minutes CR60 (c) of the chemical reaction Insets show a magnified digital

image of a droplet of the respective suspension on a 45deg inclined glass slide after 60 minutes


suspensions for different chemical reduction time (at 50 degC) The pH value of a suspension

upon the addition of with no chemical reduction step is indicated with the half-filled symbol in

(b) The corresponding zeta potential values of GO-GNP suspensions at 5 35 and 60 min of

reaction is indicated in (b)

The as-prepared GO-GNP suspensions were found to go from an initial liquid behaviour to gel

behaviour during the 60 minute reduction with an excess of L-ascorbic acid (Figure 34a)

Cone and plate rheology found that the viscosity went from 017 Pa∙s initially to 47 Pa∙s after

35 minutes reduction (CR35) and 102 Pa∙s after 60 minutes (CR60) This gelation was due to

the enhanced π-π interactions between the GO flakes after partial chemical reduction and the

reduced hydrophilic nature to prevent dispersion but left enough for hydrogen bridging which

caused the formation of a weekly cross-linked network within the suspension (Figure 34 and

35)[146147] The pH was monitored as a function of time upon the addition of acid to monitor

the reduction of the GO The initial pH value of the suspension was 39 (Figure 35 b) and it

75

dropped to 28 immediately upon the L-ascorbic acid addition After 40 mins the graphene

oxide appeared to be fully reduced and no further pH was observed De Silva et al suggested

that the functional groups such as carbonyl and carboxylate groups on GO are gradually

removed whilst consuming the H+(aq) leading to the rise of the pH to 35 with reduction

time[148]

The Zeta potential of the suspension was measured to further understand the suspensionrsquos

behaviour It was found that CR5 CR35 and CR60 was constant at -28 2 mV However the

Zeta potential has a complex dependence on both the pH and degree of reduction It is important

though in the formation of the hydrogel hence these factors were explored in more detail The

as-made GO GNP and the GO-GNP dispersions were studied as a function of pH between 2

to 4 using a 001 molL buffer solution As can be seen in Figure 35 b the studied suspensions

after chemical reduction (from 0 to 60 minutes) present pH in the investigated range At all

pHs the GO had a considerably lower value and broader distribution of the Zeta potential than

GNP in accordance to Salim et alrsquos report [149] due to their oxygen functional groups (hydroxyl

carboxyl and carbonyl) which render high density of electrical charge per unit area (Figure

36)

76

Figure 36 Zeta potential distribution for as made of GO-GNP GNP and GO suspensions as a

function of the buffer solution pH

The GO-GNP suspensions show a single peak that goes from around -175 mV for pH 2 to -

353 mV for pH 4 indicating a stable colloidal suspension especially for pH above 2[150] The

lack of a bi-modal distribution is a piece of evidence that the GO and GNP have aggregated

with each other[143] GNP have a relatively defect-free basal plane which is hydrophobic in

nature with a low surface charge measured between -12 mV and -27 mV[150][151] However

in the presence of GO sheets GNP flakes can attach to them via van der Waals and repulsive

electrostatic forces[149ndash151] leading to GO-GNP hybrid flakes with a zeta potential closer to

that of GO making it stable in water

332 Production of areogels

The CRt suspensions were then unidirectionally freeze-cast and freeze-dried to form free-

standing aerogels with both cylindrical (diameter = 2 cm) and rectangular (8cmtimes2cmtimes08cm)

77

shapes as shown in Figure 37 The CR0 samples show a density of ~332 plusmn 21 mgcm3 and

after chemical and thermal treatment the CRtTR300 samples show lower densities between

~21 gcmsup3 and ~28 gcmsup3 (Table 31) The lower density for CRtTR300 samples is due to the

removal of functional groups from GO surfaces and a lower volume shrinkage due to stronger

bonding formed by the partial chemical reduction[152]


(before and after freeze dry) and XPS spectroscopy result of C1s spectra and O1s spectrum for

CR0 CRtTR300 and CR60TR800 aerogels

Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

Figure 37 (a) Photograph of different shape CRtTR300 aerogels produced by the developed

route (b) SEM images of the cross-section perpendicular to the freezing direction of

CR0TR300 (c) the cross-sections perpendicular to the freezing direction with higher

magnification (d) cross-section parallel to the freezing direction (e) SEM images of the cross-

section perpendicular to the freezing direction of CR35TR300) (f) the cross-section

perpendicular to the freezing direction with higher magnification (g) cross-section parallel to

the freezing direction (Red circles and arrows in the images indicate the freezing direction)

The internal structure of the network consisted of long microscopic channels oriented parallel

to the ice growth direction and separated by thin walls that were formed by the rearrangement

of GO and GNP flakes between ice crystals during freezing (Figure 37) Although the weight

ratio of GNP is much higher than GO (41) due to the large specific area from the oxide thin

flakes the aerogels scaffold is mainly formed by GO while thick GNP flakes are found amidst

the network (Figure 37 cf ) The aerogels produced from the suspensions that undergo a partial

reduction step of 35 min (Figure 37 e-g ndash CR35TR300) resulted in the formation of more

defined elongated lamellar pores that extend across larger domain areas as compared to

CR0TR300 samples (Figure 37 b-d) Form the cross-sectional SEM images of the aerogels

79

produced with Figure 37 b and without Figure 37 e partial reduction step it can be seen that

chemical reduction helps in the formation of more defined lamellar channels and extend across

larger areas The freeze-casting process is governed by complex and dynamic liquid-particle

and particle-particle interactions Other studies have previously reported that the oxygen

content is one of the factors that can affect these interactions[153] The degree of reduction of

GO colloids before freezing controls the surface characteristics of the flake[146] which in-turn

can influence the flake-flake interactions promoting the network formation andor their

rejection from the freezing front[153] During freeze-casting as the ice crystals grow

anisotropically both GO and partially reduced GO suspensions can stabilize the GNP in water

allowing the freeze-casting technique to create homogeneous porous networks As partially

reduced GO sheets are less hydrophilic and more rejected than non-reduced GO those are

forced to align along the moving solidification front concentrating and squeezing at the crystal

boundaries and yielding a highly ordered layered assembly[153154] As a result a more

anisotropic structure can be obtained when some partial chemical reduction is employed before

processing However longer chemical reduction periods leads the suspensions to become too

thick (Figure 34 and 35) hindering the mobility of the solid phase within the suspension

during freezing and strongly influencing the final microstructure of the aerogels[153][155]

(Figure 38)


80

rGOTR300 (b) cross-section parallel to the freezing direction of rGOTR300 (c) cross-section

perpendicular to the freezing direction of CR60TR300 (d) cross-section parallel to the freezing

direction of CR60TR300 the cross-section perpendicular to the freezing direction with higher

magnification (g) cross-section parallel to the freezing direction Red circles and arrows in the

images indicate the freezing direction

Raman spectra of the rGO region of final aerogels are shown in Figure 39 a The as-prepared

GO exhibits typical features from graphene oxide materials for example the G band (~1580

cm-1) has a similar intensity to the D band (~1350 cm-1) (IDIG~1)[156] The D band signature

is associated with structural defects and the partially disordered structure of graphitic domains

The intensity ratio IDIG decreases from ~089 for CR0TR300 to ~062 for CR35TR300 and

~041 for CR60TR300 Figure 39 b shows how the IDIG ratio varies as a function of partial

chemical reduction time It can be observed that the L-ascorbic acid has a significant effect on

removing functional groups reorganizing the structure of GO-GNP aerogels and leading to a

decrease in the ratio between D and G band intensities However as pointed out previously a

chemical reduction time too long will increases the viscosity even further starting to transform

the suspension into a gel (Figure 34 and 35) and significantly restricts the solid phase mobility

reducing the anisotropy as that can be observed from sample CR60TR300 (Figure 38)

81


(CR0TR300 CR35TR300 and CR60TR300 aerogels) and starting GO and GNP (b) IDIG

ratio (Intensity ratio of D band and G band from Raman spectroscopy) for CRtTR300 aerogels

with rGO region as a function of partial chemical reduction time (c) XPS survey spectra were

undertaken on CR0 and CRtTR300 aerogel samples (CR0TR300 CR35TR300 and

82

CR60TR300 aerogels) starting GO and GNP


CR35TR300 samples and (d) CR60TR300 samples

XPS spectroscopy was also employed to investigate the chemical structure and composition of

the as-prepared GO GNP and aerogel samples For GO CRt and CRtTR300 samples four

distinct peaks associated with sp2 C=C (2845 eV) C-O (2864 eV) C=O (2881 eV) and O-

C=O (2885 eV) were observed (Figure 310) The CO atomic ratios have increased from 15

for GO to 42 for the CR0 mixture (Table 31) due to the additional GNP All treated samples

show a considerable decrease in the intensity of oxygen-contained groups at a binding energy

of 2868 eV indicating the successful reduction of the GO After thermal treatment the sample

CR0TR300 presented a CO atomic ratio of 108 Meanwhile the CO ratio of the samples that

underwent a pre-partial chemical reduction CR35TR300 and CR60TR300 increased to 142

and 158 respectively The XPS results confirm the analysis from Raman spectra that with the

help of chemical reduction oxygen-containing functional groups are better removed from the

83

surface of GO and result in a better reduced final product Figure 310 shows an extract of the

XPS region of C 1s binding energies (280 ndash 298 eV) where it is also possible to see the decrease

of oxygen-containing groups with the increase of chemical reduction time

Figure 311 Water contact angles for rGO (rGOTR300) and rGO-GNP aerogels (CR0TR300

CR35TR300 and CR60TR300)

Another property of interest of aerogels is their wettability For example hydrophobic

graphene-based aerogels have shown promising potential as efficient oil absorbent self-

cleaning and anti-icing materials[157] However due to the hydrophilic nature of GO GO-

based aerogels generally show relatively high hydrophilicity demanding further high-

temperature thermal reduction processes to tune this property Alternatively Figure 311 shows

that the addition of GNP resulted in the increase of WCA value from 506deg for pure rGO to

702deg for rGO-GNP (both treated at only 300 degC) due to the hydrophobic nature of GNP As the

treatment time for partially chemical reduction is increased the WCA increased and reached

1068deg for CR60TR300 being the highest among all the samples The increase in

hydrophobicity of the aerogels is mainly due to the reduction in oxygen-containing functional

groups on GO as the result of the chemical and thermal reduction as indicated by the XPS and

the Raman results

84


modulus and strength of CRtTR300 aerogels for different chemical reduction times (c)

Electrical conductivities of CRtTR300 aerogels for different chemical reduction times

The compressive stress-strain curves (Figure 312 a) can be divided into three parts linear

elastic yielding and recovery parts SampleCR35TR300 reaches its yielding region at around

7 compressive strain which is much earlier compared to 15 from both samples

CR60TR300 and CR0TR300 Furthermore the samples CR35TR300 and CR60TR300 show

improved recoverability after experiencing large strains compared to non-chemically treated

sample CR0TR300 (Figure 312 a) The compressive modulus of CRtTR300 samples (Figure

312 b) was estimated from the stress-strain curves (Figure 312 a) The results show the

compressive modulus improves as the chemical reduction time of suspensions increases up to

an optimum at 35 mins (CR35TR300 samples) However as the chemical treatment time

increased the compressive modulus decreases down to 006 plusmn 0009 MPa for 60 mins reduction

time (samples CR60TR300) It is mostly accepted that the compressive properties and

behaviour of graphene aerogel are directly related to its density[158159] however as can be

seen a significant difference of compressive modules is found on samples with very similar

density The high compressive strength of CR35TR300 is due to its more organized lamellar

hierarchical structure compared to CR60TR300 which has more disordered structures and

relatively smaller pores (as can be seen in Figure 5e f g and S3) This kind of lamellar

structure usually results in high elasticity and mechanical robustness[104159] In order to

elucidate the effect of the chemical reduction on the properties of the aerogels we compared

sample CR35TR300 with CR0TR300 (no chemical reduction) Although ordered structures

have been obtained within aerogels with no chemical reduction their mechanical and electrical

85

properties (Figure 8 b and c) are lower as compared to the chemically reduced samples The

chemical reduction step can contribute to the formation of a stronger network of partially

reduced flakes before the freeze-casting step[60] It has also been shown to contribute to the

restoring of the sp2 network and reducing the number of defects on GO flake[105]

Consequently besides the ordered lamellar architectures these effects can also contribute to the

properties of the aerogels

The conductivity of rGO-GNP aerogels has increased from 065 Sm with no chemical

reduction for sample CR0TR300 (IDIG ratio of 089) to 423 Sm for CR60TR300 (IDIG ratio

of 041) This behaviour can be attributed to the restoration of the sp2 carbon network

facilitating the electrons transfer within the network[160]

Figure 313 The electrical conductivity of CRtTR300 (with t minutes chemical reduction and

300 degC thermal reduction for 40 minutes at Ar atmosphere) CRtTR800 (with t minutes

chemical reduction and 800 oC thermal reduction for 40 minutes at Ar atmosphere) and rGO-

EEG CRtTR800 (GO with electrically exfoliated graphene at t minutes chemical reduction and

800 oC thermal reduction for 40 minutes at Ar atmosphere) (a) and compressive modulus of

CRtTR300 samples (with t minutes chemical reduction and 300 oC thermal reduction for 40

minutes at Ar atmosphere) developed in this work in comparison to literature values for other

nanocarbon-based materials Reduced-graphene cellular network[161] CNT foam[162]

reduced graphene-based aerogel[99] CVD graphene foam[163] graphene elastomer[153] 3D

printed graphene[164] 3D graphene macroassembly[99] 3D printing graphene[165] GO

aerogel[106] rGO-GNP hydrogel[166] and rGO aerogel[104153167168]

For graphene aerogels several studies show that the electrical conductivity can be related to

the thermal reduction temperature and bulk density[161165169] Figure 313 shows a

86

comparison between the electrical conductivity and compressive modulus obtained for the

aerogels developed in this work and data from the literature One can observe that rGO-GNP

samples show a tunable mechanical and electrical property without changing the density

Furthermore additional tests were made by increasing the thermal reduction temperature to

800 oC increasing GNPGO ratio and using electrochemically exfoliated graphene (EEG)

instead of GNP (Figure 314) It is observed that the electrical conductivity of samples

increased to 774 Sm when the higher thermal reduction was employed Increasing the GNP

content (GNP GO mass ratio of 18) in the samples considerably increases their density (~384

mgcm3) and electrical conductivity (1147 Sm) Finally GO was also shown to be able to

disperse other poor dispersibility graphene-based materials such as EEG Following the same

protocol presented in this work rGO-EEG aerogels were produced showing greater electrical

conductivity (1318 Sm) with ~368 mgcm3 density as can be seen in (Figure 314)

Figure 314 The electrical conductivity of CRtTR300 samples

34 Conclusion

In this work a simple and scalable route to fabricate rGO-GNP hybrid lamellar architectures

by combining partial chemical reduction and unidirectional freeze-casting followed by a final

heat treatment step has been developed GO was shown to effectively stabilise GNP in aqueous

87

dispersions allowing controlled freeze-casting of the hybrid system The partial chemical

reduction was used to control flow properties and flake-flake interactions and the freeze-casting

process creates highly anisotropic structures The partial chemical reduction time is shown to

impact both the electrical and mechanical properties of the obtained aerogels The CR35TR300

samples (chemical reduction for 35 minutes) exhibited the highest compressive modulus (051

plusmn 006 Mpa and strength of 0028 plusmn 00026 Mpa) amongst all the samples with great

recoverability after the large strain of 35 By adjusting the processing and formulation

parameters the aerogels microstructure CO ratio and properties can be fine tuned for a wide

range of applications The protocol reported in this work can also be applied to other graphene-

based materials Electrochemical exfoliated graphene was used here as a proof-of-concept

demonstrating the practical opportunities in the development of lightweight graphene-based

lamellar architectures for functional and structural applications

88

4 Chapter 4 rGOGNP aerogel based epoxy composites

for Joule heating applications

In this Chapter the reduced graphene oxidegraphene nanoplatelets hybrid aerogels were

infiltrated with epoxy resin to create rGOGNP aerogel epoxy nanocomposites The synergistic

effect of GNP on the intrinsic properties of the graphene-based aerogel and hence aerogel

composites such as glass transition temperature electrical conductivity thermal conductivity

and mechanical properties are tuned and investigated Benefiting from the 3D graphene-based

network great dispersion and an improved grapheneepoxy resin interface the composite with

the highest GNP content shows excellent Joule heating performances with a steady-state

temperature of 213 degC at the relatively low applied voltage of 5V and excellent cycle life The

study also show that the Joule heating induced steady-state temperature follows a linear

relationship with both the electrical and thermal conductivities of materials The obtained

results indicate that the epoxygraphene-based aerogel composite can be a promising material

for thermal management applications

89

41 Introduction

Electric heating systems have been used over a century across a wide range of

applications including local heating automotive de-icing drug release and

micropatterning[170] Electrothermal materials are used in this context to convert

electrical energy into heat energy via Joule heating Such materials must possess

resistive behaviour good thermal conductivity high-temperature sensitivity low

energy consumption and good cycle stability[171][172] Traditionally heavy metal

alloys are used for Joule heating applications which are very dense costly prone to

oxidation and incompatible with polymer composites Noble metals are also used for

this purpose[173] but they fail to meet the growing demands in heating performance

due to their high cost Thus carbon-based materials have received significant attention

due to their attractive features such as energy-efficiency and excellent

thermalelectricalmechanical properties[174][175][176][177][178] Unfortunately

these materials have a few shortcomings which lead to unsatisfactory performance

when used for electrothermal applications For instance randomly oriented

nanostructures fail to exhibit good mechanical properties electrical stability and

consume higher energy when used as a heating element[93] Laser-induced reduced

graphene oxide (rGO) can attain a temperature of 135 degC at a relatively high applied

voltage of 9 V with 30 A current[179] It has been seen that the steady-state temperature

can be increased with applied voltage[180] which is unlikely and unsafe

The excellent electrical and thermal properties from rGOGNP hybrid aerogel as

evidenced in Chapter 4 can be a suitable 3D scaffold for polymer composite

preparation and accomplished for Joule heater with uniform heating properties

compared with conventional method such as solvent mixing and sheer

mixing[178][181][110] Hence a scalable and environmentally friendly template

method is proposed in this work to fabricate 3D epoxy resin infiltrated graphene-based

aerogel composites (EGAC) where the 3D hybrid aerogel provides a template

framework and infiltrated with epoxy resin The Joule heating properties of EGAC with

90

GNP-content are explored and correlated with the changes in the morphology electrical

conductivity and thermal conductivity In order to depict the superiority of 3D EGAC

for Joule heating properties and mechanical properties the composite (epoxyGO-GNP

named as EGC) is also prepared by the standard shear mixing method and compared

42 Experimental methodology

421 Materials

The materials were used in this work are graphite flakes (grade 2369 Graphexel Ltd

UK) graphene nanoplatelets (GNP M-25 XGscience USA) with flake size of 106

microm Sodium nitrate (Sigma-Aldrich ACS reagent ge 990) KMnO4 (Sigma-Aldrich

ACS reagent ge 990) H2SO4 (ACROS Organics 96 solution in water extra pure)

L-ascorbic acid (Sigma-Aldrich L-ascorbic acid 99) epoxy resin (Araldite LY5052)

and the hardener (Huntsman Ardur HY5052) The chemicals are used as received and

without any further purification

422 Synthesis of aerogel composite

Preparation of GO solution and rGOGNP hybrid aerogel

GO flakes were produced by a modified Hummersrsquo method which is the same as in

Chapter 3[144] The hybrid rGOGNP aerogel was prepared with the same method as

in Chapter 3 with 60 minutes chemical reduction with 800 degC under argon atmosphere

for 40 minutes The resulting samples were labeled as GA-X where X represents the

weight ratio between GNPs and GO

Epoxy infiltrated graphene-based aerogel composite

Epoxy resin and hardener were mixed at a weight ratio of 10038 and infiltrated in the

GA-X under vacuum for 1 h The mixture was then precured at room temperature for

91

24 h followed by curing at 100 degC for 4 h to obtain the final composite (Scheme 41)

The images presented in Scheme 1 are the scanning electron micrograph of GO GNP

GA and EGAC The resulting samples were labeled as EGAC-X For the sake of

comparison GO and GNP with the same loading in total were added by shear mixing

and cured with epoxy resin named as EGC-X The loading of final composites was

calculated by the weight of graphene aerogel divide by the weight of composites as

125 21 3 375 and 46 wt for EGAC-2 EGAC-4 EGAC-6 EGAC-8 and EGAC-

10 respectively


Sample Starting graphene

suspension concentration

(GO in mgml3 and GNP

in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92


scanning electron micrograph of original samples

423 Joule heating characterisation

The Joule heating properties of all of the samples were conducted by applying the

voltages across the aerogel The current-induced temperature was recorded by an IR

thermal camera with a recording function Samples were inserted with a custom-made

clip and tightened enough to ensure a reliable and uniform electrical contact area The

electrical current and power applied to samples from two ends were controlled and

monitored by the DC power supply The applied voltage and delivered current were

93

restricted within 20 V and 10 A for safety purposes respectively The digital images of

the custom set-up are shown in Figure 62

424 Morphology and structure

The surface morphological images of all samples were investigated by scanning

electron microscope (SEM Ultra-55) The Raman spectroscopy of the rGO GNPs and

epoxy as well as Raman mapping of the EGAC were performed using a low-power

633 nm He-Ne laser in a Renishaw 2000 Raman spectrometer For the Raman mapping

analysis 121 Raman spectra were obtained over 50times50 microm areas of the composite

WIRE 32 software was used to deconvolute the Raman spectra of the as-received GNP

as-synthesized GO and epoxy

425 Electrical and thermal properties

The electrical conductivity of the studied samples was tested on a rectangular shape

with a dimension of 10 mm times 10 mm times 1 mm The test method is the same as in section

326

Differential Scanning Calorimetry (DSC) was performed using a DSC Q100 analyzer

(TA instruments) heating from room temperature to 200 degC at a rate of 10 degC to

determine the glass transition temperature (Tg) and heat capacity of the studied samples

Thermo-gravimetric analyses (TGA) were performed in the temperature range of room

temperature to 1000 degC at a heating rate of 10 degCmin in an N2 environment The thermal

diffusivity (120572) of samples was tested with the Laser flash technique (Netzsch LFA 467

USA) and the thermal conductivity (120582) of the sample was calculated by the following

equation

120582 = 119862119901 times 120588 times 120572 (41)

94

where Cp ρ and α represent specific heat capacity density and thermal diffusivity of

the composites respectively


For flexural properties a universal testing machine (MTS Insight 1 SL) was used

according to the specification ASTM D790 The composite samples with the dimension

of 28 mm times 3 mm times 16 mm were loaded in three-point bending with a support span of

24 mm at a cross-head speed of 20 mmmin The fracture toughness (opening mode a

tensile stress perpendicular to the plane of the crack) was measured for the edge-

notched bending samples with a support span of 24 mm and a crosshead speed of 100

mmmin according to the ASTM D5045 specification The dimension of the sample for

this case was 28 mm times 6 mm times 3 mm The fracture toughness KIC under the plane strain

condition was calculated using the following equations

1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl

[199minus119886119882frasl (1minus119886

119882frasl )(215minus393119886119882frasl +271198862

1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)

where B W Pmax and a are the sample width sample height maximum load and initial

crack length respectively aW for all samples was equal to ~05 and the dimensions

of the above sample are under the requirement of plane strain conditions At least five

tests were conducted for each sample in the fracture tests

43 Results and discussions

431 Morphological and structural analysis

The surface morphology of aerogels (Figure 42 (a-b) clearly indicate the anisotropic

porous nature of aerogel with all of the samples having highly aligned walls connected

by transverse bridges This structure results from the freeze casting process in which

the graphene flakes follow the ice growth direction and are precipitated into the crystal

95

boundaries As the GNP loading increases the walls and bridges are found to be

increased (eg Figure 42 b compared to Figure 42a) The epoxy resin is infiltrated in

the GA without disturbing the network of graphene as shown in Figure 42 c In contrast

graphene flakes in epoxygraphene composite (EGC) are randomly oriented in the

epoxy matrix (Figure 42 d) which may not be enough to provide continuous pathways

electrically and thermally

Figure 42 Morphology of aerogel composites scanning electron micrographs of (a)

GA-2 (b) GA-10 the fracture surface of (c) EGAC-2 and (d) EGC-2

Raman mapping was used to further confirm the uniformity of the graphene within the

composites (Figure 43) Initially the Raman spectra of the different components were

taken The G-peak (1586 cm-1) and Gʹ-peak (~2866 cm-1) are the signature peaks of

the graphitic structure (Figure 43 b)[182] The presence of other characteristics peaks

of defected graphene such as Dʺ (~ 1195 cm-1) D (~1328 cm-1) D (1480 cm-1) Dʹ

(~1610 cm-1) D+Dʺ (~2645 cm-1) D+Dʹ (~2929 cm-1) and 2D (~3064 cm-1) are also

observed in GO and GNP The Dʺ and D are the probe of the oxygen content of

graphene structures[183] Raman spectra of as-synthesized GO confirm the GO

structure and also indicate that GO contains a higher amount of oxygen functional

groups and structural defects than the GNP (Figure 43 b) Moreover the characteristics

96

peaks of epoxy such as CH-wagging (~ 818 and 1178 cm-1) epoxy ring deformation

(~911 cm-1) C-O stretching (~1048 cm-1 ) epoxy ring breathing (~1248 cm-1) CH3

bending (~1335 cm-1) CH2 deformation (~1452 cm-1) aromatic ring stretching (~1590

and 1609 cm-1) CH-aliphatic (~2868 cm-1) C-H aromatic (~3063 cm-1) and some more

prominent peaks are also observed (Figure 43 b)[184] The Raman mapping of EGAC-

2 as shown in Figure 42 a is in good agreement with SEM results


deformation peak of epoxy of EGAC-2 (1248 cm-1) (b) Raman spectra of epoxy GNP

and as-synthesized GO


The frequency-independent specific electrical conductivity of EGAC-2 and GA-2

confirmed their conducting nature with resistance dominating (Figure 44)[185] On the

contrary the infiltration of the epoxy (EGAC-2) showing a flat polt and around an 8

orders electrical conductivity enhancement compare with EGC-2 samples The

uniformed 3D graphene dispersion ensures the electrical percolation though out the

whole sample thus increased the electrical conductivity significantly Although the

EGAC-2 sample showing a reduced electrical conductivity of the original aerogel (GA-

2) by a factor of 2 due to its wetting separating the flakes (Figure 44a) the dramatic

increase can be observed while comparing with the neat epoxy sample The shear mixed

sample (EGC) though was insulating with the frequency-dependent electrical

97

conductivity showing the role of the aerogel in creating the continuous conducting

network in the other samples The electrical conductivity of the EGAC was found to

increase linearly with increasing GNP loadings (Figure 44b)

Figure 44 Electrical properties of aerogel composites (a) Electrical conductivity for

neat epoxy GA-2 EGAC-2 and EGC-2 with the function of frequency (b) Electrical

conductivity of EGAC with functional of graphene loadings

A comparison of electrical conductivities between EGAC samples with reported

graphene-basedCF composites electrothermal materials has been summarised om

Table 4-2 below The EGAC with 3D graphene network showing orders higher

electrical conductivities compares with conventional methods such as shear mixing

sonication three-roll milling and ball milling This is because the aerogel network

ensures the electrical percolation in the composites which allows the electrics to go

through the whole system thus increased the electrical conductivity dramatically The

EGAC samples with showing a similar electrical conductivity of 112 Sm compare to

the EPRGO aerogels samples of 11 Sm from literature[52] However the non-oxidised

graphene aerogel epoxy composites samples from the literature showing a much higher

electrical conductivity of 1226 Sm than the EGAC samples of 492 Sm from this

thesis This is because the remaining defects of the rGO flakes in the EGAC system

restrict the electrics movement and reduced the electrical conductivity

98


basedEP composites

Sample Fillers loading

(wt)

Dispersion method Electrical

conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46

Aerogel infiltration 112

492

This thesis

EPGNP 4 Three-Roll milling 15х10-3 [186]

EPRGO 01 Sonication and ball milling 7х10-4 [187]

EPGNP 11 Sonication 6х10-3 [188]

EPGO 3 Mechanical stirring 9х10-8 [189]

EPMWCNTs 20 Sonication 5х10-3 [190]

EPRGO

aerogels

14 Aerogel infiltration 11 [52]


(MWCNT Multi-wall Carbon Nanotubes RGO Reduced Graphene Oxide GO

Graphene Oxide GNP Graphene nanoplatelets)


The differential scanning calorimetric (DSC) study of as-synthesized aerogel

composites along with neat epoxy and EGC was conducted which is shown in Figure

45 a The Tg midpoint of enthalpy change was found to be 1173 degC for EGAC-2 and

112 degC for EGC-2 The relatively lower value of Tg of EGC than the neat epoxy

(~115 degC) may be attributed to the thermally-induced aggregation of the graphene

flakes Importantly it has been seen that the Tg of the EGAC is increasing with the

GNP-content and shifted by a maximum of around 15 degC for EGAC-10 (Tg = 1302 degC)

compared to the neat epoxy The observed result ensures that the polymer chainrsquos

motion is restricted by the 3D interconnected network structure of graphene[42] As a

result thermal stability and higher Tg are observed in EGAC-10 with the highest GNP

99

content which can also be correlated with the surface roughness of graphene at the

nanoscale and hence the fracture surfaces of EGAC are investigated later


with EGC and epoxy

Figure 45 b shows the TGA profile of neat epoxy EGC-2 EGAC-2 and EGAC-10

which consists of three different zones The initial decomposition with a very small

weight loss of all samples is quite obvious due to the loss of volatiles In the middle

zone an increased maximum decomposition peak temperature with 50 weight loss

(Tmax) is observed for EGACs (Tmax ~ 398 oC) than both epoxy and EGC (Tmax ~ 393

oC) It is also important to note that the weight loss for neat epoxy EGC and EGAC-

10 is found to be 895 879 and 862 This implies that the thermal stability of aerogel

composite with higher GNP content is better than the EGCs since the 3D graphene

network serves as an isolator and restricts the movement of the molecular chain of

epoxy and reduces the free volume[42][191] However compare with other studies

even with conventional methods prepared grapheneepoxy composites the EGAC

samples do not show outstanding advantages in terms of TGA results For example Yu

et al[192] managed to increased the Tmax value by 8 oC with only 1 wt additional rGO

Qiang et al[193] reported with 5 wt additional GO the GOEP composites have

increased their Tmax value by ~4 oC The improvement for the EGAC samples is not as

100

dramatic as other physical properties such as electrical conductivity thermal

conductivity and fracture toughness The reason for this still needs further investigation

Another influential factor that plays a significant role in the Joule heating properties of

the studied sample is thermal conductivity In order to estimate that the thermal

diffusivity of all EGACs was measured compared with EGC and neat epoxy and

shown in Figure 46 Like the electrical conductivities it has been seen that the

estimated thermal conductivities of EGAC using equation 41 are enhances

proportionally with the GNP content Specifically the improved thermal conductivities

of EGAC (from 032 to 11 WmK as GNP-content increases in the structure) than neat

epoxy (~02 WmK) are evidenced and shown in Figure 46 Eventually the

enhancement is 450 in EGAC-10 compared to the neat epoxy (inset of Figure 46)


thermal diffusivity of EGACs with neat epoxy


As seen from Figure 46 a the temperature-time response of the composites comprised

of an initial heating stage followed by isothermal behavior once a steady state had been

reached The composites then naturally cooled when the voltage was removed The IR

images of the sample surface in a steady-state zone are shown in Figure 46b-e The

steady-state temperature of EGAC was found to increase with the GNP-content with

101

the maximum steady-state temperature of 223 degC being obtained from EGAC-10 with

5V applied voltage at 105 A current (Figure 46) This performance compares to that

of EGAC-2 which had the lowest steady-state temperature of 475 degC with 0074 A

current The spatial variation in the steady-state temperature was found to be quite

uniform for all the samples (Figure 46 f) The composites were found to follow a linear

relationship for both current-voltage and power-voltage (Figure 46)

The performance of EGAC-10 was also evaluated under different applied voltage

Figure 46 h shows the applied voltage (V) dependent steady-state temperature (TJH)

profile of EGAC-10 which is fitted with the quadratic function equation 119879119869119867 = 1198981198812 +

1198790 where 1198790 = 20 degC and the obtained value of m is 892plusmn068 degCV2 Since the cycle

stability is another important factor here we performed repeated heatingcooling cycles

for EGACs Figure 46e confirms excellent cycle stability of EGAC-10 for reference

The Joule heating performances of EGAC-10 compared with other reported

electrothermal materials and summarized in Table 42 In summary the addition of GNP

into the graphene matrix is found to enhance Joule heating The changes in the

morphology structure and improved intrinsic properties of EGAC may be the key

factors for the improved Joule heating performances of EGAC with increased GNP-

content which is discussed in the next sections

In order to demonstrate the advantage of preparing the 3D composite using our method

(Figure 41) the Joule heating performance of the composite prepared by the

conventional shear-mixing method EGC-2 was also tested Unfortunately no

temperature rise was observed even when the maximum input voltage of 20 V This

result can be explained accordingly to Joulersquos Law

119876 = 1198942 times 119877 times 119905 (43)

where Q is the generated heating during the test i the current flow R the electrical

resistance of the specimen and t the time that specimen is subjected to Joule heating

Therefore the electrical properties of these materials play a crucial role in their Joule

heating capabilities The EGC-2 sample which was prepared with conventional

methods showing very low electrical conductivities which around 10-8 Sm (Figure 44)

102

thus no enough current flow going through during the Joule heating test under certain

power input (20V) Several studies showing successfully Joule heating results for

conventional method prepared graphene-based epoxy nanocomposites by increasing

the electrical conductivities by increasing the loading of graphene as well as the power

input For example Saacutenchez-Romate et al [194] managed to heated GNPepoxy

nanocomposites up to 85 degC at 8wt GNP loading with 200 V power input However

such a high power input was considered unsafe based on current lab conditions

Figure 47 Joule heating properties of aerogel composite (a) Surface temperature

103

versus time showing the heating zone steady-state zone and cooling zone of aerogel




relationship for EGAC-10 (h) steady-state temperature vs applied voltage for EGAC-

10 with fitting by quadratic equation and (i) cycle test of EGAC-10 at an applied voltage

of 5V

To further understand the reason for Joule heating properties improvement the Joule

heating induced steady-state temperature (119879119869119867) is plotted against electrical conductivity

(120590) as shown in Figure 47a and found that it follows the linear relationship via the

relation[195]

120590 prop ln (119879119869119867) (44)

Like electrical conductivity the Joule heating induced steady-state temperature (119879119869119867) is

also related linearly with thermal conductivity (λ) as shown in Figure 47b Figure 47

c summarizes the relationship of property-performances which reveals that constructing

a 3D network of graphene facilitates isotropic responses and hence excellent thermal-

electron transportation unlike the 1D and 2D nanostructures where the alignment is

crucial Figure 47d indicates the superiority of epoxy infiltration in the graphene

aerogel matrix to improve electrothermal properties compared to the other existing

approaches

Based on the above-obtained results the improved Joule heating performances of

EGACs with the GNP content can be explained as follows (1) The 3D porous structure

of rGOGNP fillers provides a uniform dispersion of fillers in an epoxy matrix and

improved electrical and thermal properties hence improve the Joule heating properties

(2) GNP increased the graphene loading for composites thus increased electrical and

thermal properties and hence the better Joule heating performance has been obtained

The EGAC samples showing great isotropic Joule heating properties due to the GNP

104

aerogels isotropic nature The anisotropic Joule heating properties of EGAC samples

have not been tested and discussed here due to time limits However the Joule heating

properties would be expected to show differences such as heating rate steady-state

surface temperature etc in different directions As the freeze casting method created

high isotropic graphene alignment the current flow going through electrical and

thermal conductivities will not keep consistent in different directions thus influence the

Joule heating properties

Figure 48 (a) plot of steady-state temperature with electrical conductivity of EGACs

(b) plot of steady-state temperature with thermal conductivity of EGACs (c) Radar plot




from the Ref [196]


The flexural modulus flexural strength and fracture toughness of EGAC are measured

105

and shown in Figure 48 An increasing trend in flexural modulus of EGACs with the

GNP-content is observed The EGAC-10 sample exhibits the highest flexural modulus

which has been enhanced by 654 compared to neat epoxy However the flexural

strength drops after initial additional graphene loadings and indicates the brittleness of

grapheneepoxy composites Although the EGAC-8 sample shows the highest flexural

strength with a 287 increment compared to epoxy EGAC-10 shows slightly lower

flexural strength than the EGAC-8 This implies that the loading of GNP beyond a

certain limit may deteriorate the flexural strength of the composite The model I fracture

toughness of these composites has been studied using the single-notch bending

geometry[197] and the stress intensity factor (K1c) is shown in Figure 48 The

calculated K1c of EGAC-2 EGAC-4 EGAC-6 EGAC-8 and EGAC-10 according to

Equation 3 are 695 788 823 899 and 963 MPam) which corresponds to an

improvement of 309 484 549 719 and 814 respectively as compared to

the neat epoxy sample


strength and fracture toughness of neat epoxy and EGACs

In order to probe insights The SEM images of the fracture surfaces of the neat epoxy

and EGAC samples are shown in Figure 49 One of the most important failure

mechanisms in grapheneepoxy composites is the crack pinning normally proved by

106

crack front bowing while resisted by rigid nanofillers[198199] However there is no

obvious evidence of crack pinning in our EGAC samples (Figure 49 a-c) This scenario

is similar to existing reports on the 3D graphene network epoxy composites

[52112113] Moreover the presence of graphene is evidenced as a curved surface with

folded and blended flakes for our EGAC samples (Figure 42 c and Figure 49 a-c) The

good dispersion of the flakes can be found in the matrix for all our EGAC samples even

for the EGAC-10 sample To propagate cracks need to breakovercome the

interconnected walls where the walls contain multilayer graphene flakes During the

crack propagation the crack front may be blunted and deflected upon encountering the

graphene walls leaving behind significantly increased fracture surface area with a

rough surface and leading to greater energy absorption than in neat epoxy[199200] As

the GNP loading increased the crack needs to break or overcome a much thicker

graphene wall leaves a rougher fracture surface (Figure 49 (a-c)) requires more energy

to dissipate thus improves the fracture toughness The interfacial debonding may also

contribute to fracture energy absorption of the composites and the crack shows a ldquostair-

likerdquo feature in Figure 49 b The debonding may be caused by the interfacial adhesion

arising from the noncovalent bonding mechanisms like hydrogen bonds and π-π

interaction operating at the interface without functionalized rGO and GNPs[201202]

The thickness between ldquostairsrdquo is similar to the distance between the two adjacent

aligned graphene layers in Figure 42 b In comparison the neat epoxy fracture surface

is smooth and featureless which is typical for thermoset polymers after a brittle fracture

(Figure 49 d)

107


EGAC-4 with different magnification and (d) EGAC-10

44 Conclusion

Multifunctional properties such as electrical thermal Joule heating and mechanical

properties of the epoxygraphene-based aerogel composites are investigated in this

chapter In order to improve the efficiency of epoxy resin as an electrothermal heater

the graphene-based aerogel was synthesized first by freeze-casting techniques followed

by chemical-cum-thermal reductions and used as a scaffold The interconnected 3D

structures electrical conductivities and thermal conductivities are tuned by graphene

nanoplatelets (GNP) incorporation into the graphene oxide (GO) aqueous dispersion

The main conclusion drawn from our study are as follows

1 Addition of GNP in GO aqueous solution increases the density of graphene walls and

graphene bridges in the aerogel structure leading to a more interconnected porous

network of graphene Both the graphene walls and graphene bridges are served as a

108

nanoheater

2 The 3D graphene-based aerogel network provides efficient thermally and electrically

conductive pathways along with all three directions and accommodates polymers to be

infiltrated effectively

3 Both the graphene bridges and graphene walls serve as an isolator and mass transport

barrier inside the polymer matrix and hence improved glass transition temperature and

better thermal stability are observed from EGAC

4 Due to the GNP incorporation in the graphene structures the thermal diffusivity

thermal conductivity electrical conductivity and mechanical properties of the aerogel

composites are improved significantly As a result the outperformance of EGAC over

the shear-mixed epoxygraphene-based composites is evidenced

5 The above-mentioned factors are attributed to the improved Joule heating

performances of EGAC with higher GNP content

Therefore this work provides a promising methodology to construct 3D polymer2D

materials nanocomposites with improved electrothermal and mechanical properties

which can open an avenue in energy storage electromagnetic interference microwave

shielding biomedical and thermal applications

109

5 Chapter 5 Hierarchical graphene aerogel

interpenetrated-carbon fibre polymer composites

In this Chapter graphene nanoplatelets are replaced by continuous carbon fibre (CF)to

create 3D interconnected graphene oxide (GO)carbon fibre structure to improve the

electrical conductivity and mechanical properties of its final epoxy composites Here

continuous carbon fibres (CF) were infiltrated with graphene oxide (GO) solution

followed by unidirectional freeze casting to create a GO aerogel reinforced hierarchical

CF structure and infiltrated with epoxy resin is infiltrated into the as-prepared 3D

composites The final composite offers superior mechanical (288 improvement in

toughness) and electrical conductivity (624 increase in in-plane and 3300 in out-

of-plane direction) which are among the top of the reported values It is simple scalable

and environmentally friendly hence it is envisaged that it will find wide applications

in the manufacturing of next-generation multifunctional composites

51 Introduction

Carbon fibre reinforced polymer composites (CFRPCs) are used in a wide range of

industries including aerospace automotive and sporting goods due to their high

strength and stiffness [203] However the performance of these CFRPCs is limited by

their relatively poor interlaminar properties which gives rise to low toughness and out-

of-plane conductivity In recent years the nanoscale reinforcement of the matrix has

been investigated as a solution to these challenges with a focus on carbon

nanomaterials In particular graphene-related materials have shown promise due to

their 2D nature allowing more facile processing than nanotubes [204] For example

Bortz et al [205] found that the addition of 01 wt loading of GO in CFRPCs

increased the flexural strength by 25 Watson et al [206] found a 10 increase in

Youngrsquos modulus and flexural modulus of GOCF epoxy composites compared to the

original epoxycarbon fibre composites GO in a reduced state has also been found to

110

improve conductivity with Chen et al obtaining an electrical conductivity of 7 Sm-1 at

the frequency of 8 GHz[207] However one difficulty with graphene-related materials

is obtaining a good dispersion of them within the CFRPCs

Typically the GO is dispersed in the matrix prior to introduction into the CF lay-up

Adak et al [208] managed to increase the critical stress intensity factor (K1c) 33 with

02 wt rGO loading for CFRPCs However this approach means that the GO can

aggregate or can filter during resin infusion processing An alternative approach to pre-

disperse the GO into the required architecture prior to the matrix introduction similar

to that approach taken with the CF plies Such an arrangement can be obtained by using

a graphene aerogel (GA) which is a new class of 3D cellular interconnected material

with ultra-low density (296 mgcm3) and possess both a high surface area (584 m2g)

and electrical conductivity (~ 1 times 102 Sm) [209] The GA can be achieved with

different approaches such as 3D printing [58] chemical reduction [52] and direct

templating [210] Amongst all the methods the freeze-casting technique offers the most

versatility due to the facile control of ice crystal growth [12]ndash[14] Such GA has been

used as sole reinforcement in a polymer composite Wang et al [51] demonstrating that

intrinsic particle connectivity within GA-epoxy composites led to ultralow electrical

percolations of 0007 vol The same group also reported with only 05 wt of

graphene loading GA-epoxy composites had a 113 improvement in fracture

toughness [52] Han et al infiltrated a GA produced by freeze casting to increase 69

of fracture toughness in the epoxy matrix by 011 vol and final composites also

showing 008 Scm electrical conductivity

The improvements observed in GA-epoxy composites in both toughness and

conductivity imply that GAs could bring considerable out-of-plane and interlaminar

benefits if they were used in combination with conventional carbon fiber (CF)

composites Thus in this work carbon fibre fabrics were infiltrated with GO aerogels

to give a uniform dispersion and good alignment of GO flakes perpendicular to the CFs

Some of these infiltrated GA-CF fabrics were then heat-treated to reduce the GO in

order to improve the electrical conductivity of the GO Finally the GA-CF fabrics were

111

infiltrated by epoxy and cured The fracture toughness and electrical properties of the

final composites were evaluated and compared to composites produced by the typical

route of infiltrated GO-filled epoxy into the fabrics

52 Experimental

521 Materials

Graphite flakes (grade 2369 Graphexel Ltd UK) sodium nitrate (Sigma-Aldrich ACS

reagent ge 990) potassium permanganate (KMnO4 Sigma-Aldrich ACS reagent

ge 990) sulphuric acid (ACROS Organics 96 solution in water extra pure)

hydrogen peroxide (H2O2 Scientific Laboratory Supplies 35 solution in water 100

volumes) epoxy resin (Araldite LY5052 Huntsman) and hardener (Aradur HY5052

Huntsman) were used as received The polyacrylonitrile-based (PAN) carbon fibre

[090] woven fabric (T300 Toray Industries) with a filament count of 3 K was used as

the main reinforcement

Preparation of the GO solution


Chapter 3 [213]

522 Preparation of the reduced graphene oxide aerogel reinforced carbon

fibre (rGOA-CF) composites

Graphene oxide aerogel interpenetrated-carbon fibre (GOA-CF) was prepared by

infiltrating the CF with the GO dispersion and then using unidirectional freeze casting

to create an aerogel in-situ (Figure 51) 12 layers of carbon fabric (40 times 15 mm) were

manually layered up in [090] orientation and then infiltrated with 5 mgml GO

dispersion with the aid of a vacuum for 10 minutes to make ensure full infiltration (10

ml GO dispersion per gram of fabric used) The GO infiltrate fabric was then placed

directly onto the surface of the freeze caster and the GO suspension frozen in-situ by

unidirectional freeze casting The resulting frozen GO-CF materials were then freeze-

dried to remove water crystals and leave GOA-CF The reduced graphene oxide aerogel

112

reinforced carbon fibre (rGOA-CF) was prepared with the same method but was

followed by 800 thermal treatment under Argon inert atmosphere for 40 minutes to

remove functional groups and improve its electrical conductivity It is noted that this

heat treatment would also affect the CFrsquos sizing as well as the functional groups of the

GO Composites were produced by vacuum bag infiltration of the GOA-CF and rGOA-

CF with the epoxy resin and hardener mixed at a weight ratio of 100 38 The epoxy

had fully infiltrated the CF after 2 hrs after which the vacuum was removed and

composites were left to partially cure at room temperature for 24 hrs Curing was then

completed in an oven at 100 deg C for 4 hrs For comparison GO reinforced CF

composites were produced by infiltrating the GO into CF cloth as before but then

drying the samples in an oven rather than freeze casting and freezing drying Thus these

composites are comprised of GO dispersed around the fibres and not arranged as an

aerogel Finally a control CF-epoxy composite with no GO was produced

In this Chapter the samples are denoted as CFEP for pure CFEP composites GOA-

CFEP for GOA reinforced carbon fibre epoxy composites rGOA-CFEP for rGOA

reinforced carbon fibre epoxy composites oven-dried GO-CF for GO reinforced CF

epoxy composites without freeze casting technique and CFEP for the control

The masses of the composites were recorded at each step of production to measure the

relative weight loadings of each component The final GOA-CFEP rGOA-CFEP and

oven-dried GO-CF composites comprised 325 vol CF 1 vol GO and 665 vol

epoxy resin for the samples The CFEP comprised 305 vol CF and 695 vol

epoxy resin (The densities of the GO rGO CF and epoxy were taken as 180 191

176 and 117 gcm3 respectively)

113

Figure 51 Schematic illustration of GOA reinforced CFEP composites preparation


The Joule heating characterisation methods are the same as in section 423 The digital

images of the custom set-up are shown in Figure 62

524 Morphology and microstructure

The morphological and microstructure of the specimens are the same as in section 424




326

114


The mode 1 fracture toughness has been tested with the same method as section 426

according to ASTM D5045 standard

53 Results and discussion

531 GO and rGO powders


GO flakes width distribution (c) AFM image of GO flake from dispersion obtained by

drop-casting (d) Height profiles of the selected section labelled as 1 in Figure (c)

Figure 52 shows the prepared GO flakes on the silicon substrate It can be seen that the

flakes are quite flat and free of wrinkles which facilitates their flattening during the

preparation of aerogel to ensure a durable network Since the mild condition was used

in the preparation the GO flakes have an average flake size of ~10 microm in diameter

115

with some large flakes ~50 microm also seen (Figure 52 b) In addition the GO flakes are

mostly monolayers or bilayers as confirmed by AFM[214] and a typical one is shown

in Figure 52 c


spectroscopy for GO powders and rGO powders

Raman spectra of samples are shown in Figure 53 a The as-prepared GO exhibits the

D band (~1580 cm-1) has a slightly higher intensity than the G band (~1350 cm-1)

(IDIG~13) which is typical features from graphene oxide materials[156] The D band

signature is associated with structural defects and the partially disordered structure of

graphitic domains However after the thermal reduction there is a dramatic decrease

in D band intensity and this decreased the IDIG to ~047 In addition the 2D band

(~2700 cm-1) that appears after thermal reduction indicates the restoration of the sp2

network which indicates the increase of interaction between graphene flakes The XPS

spectroscopy has been employed to investigate the effects of thermal reduction further

the rGO sample showing a considerable decrease of the intensity of oxygen-contained

groups at a binding energy of 2868 indicating a successful reduction of the GO

Meanwhile the CO ratio has been improved from 15 for GO to 87 for the rGO as the

most oxygen contained has been removed from the GO surface

532 GOA-CF and GOA-CFEP composites

116



red arrows indicated freeze direction)

The microstructure of CF GOA-CF and over dried GO-CF was studied by scanning

electron microscopy (SEM) and is shown in Figure 54 The pure carbon fibres

consisted of well aligned fibres ~ 7 microm in diameter The GOA was found to

successfully form within the CF with the GO flakes bridging and separating the CFs

(Figures 54 b and c) The thin GO sheets were oriented vertically along the CF

direction and forming the bridges between CF (Figure 54 b and c) This orientation is

due to the growth of ice crystals parallel to the CF direction The ice growth then

follows highly anisotropic along the moving solid front and it will be concentrated and

then squeezed at the crystal boundaries which yield a highly ordered layered assembly

[102] As a comparison the conventional oven-dried GO-CF (Experimental Section) in

Figure 54 d only shows that the GO sheets have been attached to CF surface due to the

electrostatic force between GO and CF and a significant agglomeration of GO flakes

can be observed

117


composites

Sample CFEP Oven-dried GO-

CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)

135 plusmn 006 130 plusmn 009 126 plusmn 004 122 plusmn 008

After the infiltration of the resin the CFEP oven-dried GO-CFEP GOA-CFEP and

rGOA-CFEP composites were cured and their density is shown in Table 51 The

density of the four materials was found to be the same within error suggesting that the

resin infiltration brought the separated fibres back together in the GO-CF samples

118




direction (b) out-of-plane direction and electrical conductivities at the frequency of 1

Hz for CFEP GOA-CFEP rGOA-CFEP and oven dried GO-CFEP composites (c)

in-plane direction (d) out-of-plane direction (e) Schematic description of

the x y and z directions in the specimens

The carbon fibre woven employed in this study is 090deg orientation and the electrical

119

conductivities of the composites laminate are different in the two Cartesian directions

Figure 55 a-b shows log-log plots of the specific conductivities with increasing

frequency for all samples of both in-plane and out-of-plane direction It can be obtained

that all samples have exhibited a plateau to a critical frequency which indicated the

formation of the conductive path has formed up in the matrix From Figure 55 c it can

be obtained the electrical conductivities of in-plane (through x-direction and y-direction)

were measured to be two or three orders of magnitude higher than that out-of-plane

(through-thickness z-direction) as displayed in Figure 55 d

The conductivity from in-plane direction depends on the conductivity of carbon fibre

itself in its longitudinal direction which results in a much higher value than out-of-plane

direction This result is from the laminated structure of composites and unidirectional

carbon fabrics nature Moreover wavy carbon fibres are used and these fibres provide

many more contact points between nearby fibres Thus a complex 3D conduction path

is formed from carbon fibres itself through the epoxy matrix contributing to the

electrical conductivities in the in-plane direction

Contrary to the in-plane direction the conduction paths through out-of-plane in the

epoxy-rich area are much less and can only depend on interlayer between carbon fabrics

Compare with control composites laminate the GOA and rGOA reinforced CFEP

systems provides 3D conduction paths between carbon fibres which provide more

conductive paths through fibres especially between carbon fibre interlayers which

increased 702 for GOA and 624 for rGOA in the in-plane direction and an increase

of 715 for GOA and 3300 for rGOA of out-of-plane direction For oven-dried CF-

GOEP composites it does not show too many differences with CFEP composites as

the 3D structure is not been assembled

A comparison of electrical conductivities between rGOA-CFEP with reported


Table 5-2 below It can be obtained with sample graphene loading at ~1 vol the

rGOA-CFEP showing tens higher enhancement in terms of its out-of-plane electrical

conductivities compare with reported values Such a dramatic improvement is due to

120

the uniform fillers dispersion from 3D graphene network in the rGOA-CFEP system


basedCF composites

Sample Process Electrical properties enhancement Ref

10 vol rGO

reinforced CFepoxy

composites

3D rGOCF constructed

based on Aerogel forming

mechanism and then

infiltrated with epoxy resin

Conductivity + 3300 This

thesis

10 wt

GNP reinforced

CFepoxy composites

Three-roll milling dispersion Conductivity + 165 [215]

GO coated CFepoxy

composites

Electrophoretic deposition

(EPD) technique for grafting

GOs to the CF followed by

vacuum-assisted resin transfer

moulding

Conductivity + 127 [216]

08 wt hybrid

nanofillers with (25

GNP 50 CNT 25

nanodiamond)

Sonication Conductivity + 172 (145 times

10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites

GNP coated on CF with 3

wt GNP in the coating

solution


1 vol GNP reinforced

CFepoxy composites Solvent-assisted dispersion Conductivity + 70 [219]

(CNT Carbon Nanotube GO Graphene Oxide PDMS polydimethylsiloxane GNP

Graphene nanoplatelets CF Carbon Fiber)


The Joule heating experiments have been performed for both GOA-CFEP and rGOA-

CFEP samples however with the maximum power input of 20V applied there is no

temperature rise can be observed from the samplersquos surface As discussed in section

434 The electrical properties play a key role in the samplersquos Joule heating

performance The samples with either too high or too low electrical conductivities may

121

not exhibit any Joule heating properties As can be obtained from section 533 the

GOA-CFEP and rGOA-CFEP samples showing a range from ~3-9 Scm in in-plane

electrical conductivities but its out-of-plane electrical conductivities only showing a

range from ~0005 ndash 0025 Scm Such a great electrical conductivity difference in these

two directions would give a non-uniform current flow thus can not raise up any

temperature for samples with this certain power input (20 V) The GOA-CFEP and

rGOA-CFEP samples could be expected to exhibit any Joule heating performance by

using a much higher power input However this assumption still needs further

investigation

535 Fracture toughness enhancement of the composites


CFEP composites (a) loading vs crack displacement (b) Normalized K1c and G1c value

by volume fraction (c) Schematic diagram of the three-point bending toughness test

In the Mode 1 fracture tests the GOA-CFEP composites exhibited the highest load

before failure and the rGOA-CFEP composites showed the longest crack length before

122

failure whilst the oven-dried GO-CFEP and control CFEP showed similar behaviour

(Figure 56 a) The K1C of oven-dried GO-CFEP GOA-CFEP and rGOA-CFEP were

calculated as 283 348 and 326 MPam according to (Eq 52) given a corresponding to

an improvement of 47 288 and 206 respectively as compared to that of the

control CFEP

To further understand the fracture behaviour of the samples (Figure 57) the fracture

surfaces of the samples were studied using SEM The matrix is quite different from that

of a pure epoxy where typical flow patterns are observed (Figure 57 a b) rough surface

is thought to be the structure of GO aerogel in the cured matrix When crack encounters

the GO flakes cracks possibly bifurcate and grow at the vicinity of flakes[198]

However the convergence of cracks when they pass over the GO flakes may not be

easy as it is prohibited by the further network of GO aerogel that connects the GO

flakes[217] Therefore the formation of numerous microcracks occurs and they are

thought to be random as well following the random alignment of GO flakes[220] They

all follow a very tortuous path when propagating in the matrix therefore a much-

increased surface area This along with the oxygen functional groups that improve the

interfacial adhesion remarkably increases the interfacial energy dissipation This

formation of microcracks has also been observed in other epoxy systems when they

were toughened by functionalized graphene[220] However the GO flakes are probably

too thin to deflect the very large crack which may break the network hence a relatively

flat but rough fracture surface can be seen Such large improvement in K1C at this GO

concentration as compared to GNP[221] can be attributed to the less likely of flake

separation as a result of the much higher interlayer bonding and thin thickness This is

beneficial as separation of flakes will further lead to crack sharpening that results in a

decrease of K1C[221]

123


composites (arrow indicate fracture direction) and (d) CFEP composites

In addition the enhanced interface between epoxy and CF also contributes to the

improved toughness as evidenced by the residual epoxy around CF after a fracture As

can be seen in the specimen prepared in the oven method with only CF (Figure 57 d)

CF has smooth surface indicating that the cracks primarily propagate around the CF

that left a smooth CF surface due to the relatively poor interface In contrast GO aerogel

has improved the interfacial adhesion with matrix and effectively anchored the epoxy

resin (Figure 58 a) The cracks are then forced to propagate along a more torturous

path

124

Figure 58 Schematic diagram of the crack propagation and suppression behaviour of

(a) CFEP laminate (b) GOA-CFEP laminate (c) oven-dried GO-CFEP

Thus the proposed mechanism for observed toughening is summarized schematically

in Figure 58 The improvement in oven-dried CFEP composites can be due to the

addition of GO flakes at the fibre-matrix interface that leads to crack deflection or

pinning around the GO flakes as well as the potential improvement in interfacial

adhesion[3][21] However the improvement is not significant due to the heavy

agglomeration of GO flakes (Figure 54 d) [223] In contrast the additional freeze

casting process offers significant enhancement in both K1C and G1C due to the following

reasons

(1) Uniform dispersion leading to significant crack deflectionmicrocracking in the

matrix

(2) Alignment of the GO

(3) Aerogel network ensures a more homogenous toughening of the whole system

A comparison of mechanical properties between GOA-CFEP with reported graphene-

basedCF composites electrothermal materials has been summarised om Table 5-3

below The GOA-CFEP samples showing a 288 K1c improvement which is more

than 3 times higher than the GO reinforcd CFEP with conventional method However

the K1c improvement of GOA-CFEP is not as good as some pristine graphene and

CNT reinforced CFEP composites This is may due to the extra defects from GO

surface which decrease the mechanical properties


basedCF composites

Sample Process Mechanical properties

enhancement

Ref

10 vol GO

reinforced CFepoxy

3D GOCF constructed based on

Aerogel forming mechanism

K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites

Shear mixing G1c + 56 [224]

2 vol GNP

reinforced CFepoxy

composites

Mechanical stirring G1c + 24 [225]

10 wt GNP

reinforced CFepoxy

composites

Three-roll milling dispersion G1c + 62 (1914 to

2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)

Sonication K1c + 53 [217]

02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites

Ultrasonication G1c + 53 [226]

05 wt GNP CF

reinforced epoxy

composites

Mechanical mixing G1c + 481 [227]

025 wt GO

reinforced CFepoxy

composites

Sonication G1c + 81 [228]


Graphene nanoplatetes CF Carbon Fiber)

54 Conclusion

Graphene aerogel reinforced carbon fibres epoxy systems by unidirectional freeze

casting was shown to be an efficient technique to develop hierarchical reinforcement in

multi-scale laminated composites which improved the mechanical toughness and

electrical conductivity The whole processing was environmentally friendly with no

toxic solvent or chemicals involved The model I toughness KIC has been improved by

126

288 and the critical strain energy release rate GIC improved by 676 for GOA-

CFEP composites The electrical conductivity has improved for 624 and 3300

along and transverse to the fibre directions respectively This concept for 3D graphene

structure to improve mechanical and electrical properties for CFPRCs could open a new

opportunity for CFPRCs materials and their potential applications for aerospace

automotive and sports industries etc

127

6 Chapter 6 Epoxy resinTi3C2Tx MXene Aerogel

Composites for Electrothermal Applications

This Chapter is focused on using MXene another emerging 2D material as a scaffold

to design epoxy resinMXene aerogel composite Here 3D epoxy resinTi3C2Tx MXene

composites are synthesized using the unidirectional freeze-casting technique to prepare

an anisotropic Ti3C2Tx aerogel and followed by vacuum infiltration of epoxy into the

aerogel Morphology and structure of as-prepared aerogel composite are systematically

investigated by scanning electron micrograph X-ray micro-computed tomography

(microCT) X-Ray diffraction method electrical and thermal conductivity and X-ray

photoelectron spectroscopy Joule heating properties of aerogel composites are

evaluated and compared with bare MXene aerogel and shear-mixed epoxyMXene

composite The epoxyMXene aerogel composites prepared in a simple and cost-

effective manner are anticipated as a potential alternative to the traditional metal-based

and nanocarbon-based electrothermal materials

61 Introduction

As discussed in Chapter 4 there is a need of designing a suitable composite to obtain a

high electrothermal response where aligned nanostructures may provide thermal

transportation pathways and polymer matrix can dissipate the heat effectively at low

driven voltage is the focus of this work With metal-like high conducting features

(electrical conductivity ~106 Sm) and excellent thermal properties MXenes a family

of 2D transition materials of metal carbidenitridecarbonitride[229][230][231][232]

may offer promising electrothermal properties[233][234] 3D porous macrostructures

of MXenes offer outstanding performance mostly in energy applications[235][145] It

is also reported that simultaneous in-plane heat dissipation and cross-plane heat

insulation can be obtained from MXene films[59] Therefore 3D MXene may be a good

128

candidate for elements in an electrothermal heater however unwanted terminal groups

produced during the synthesis are well-known to degrade the stability of MXenes and

can have a negative impact on their Joule heating performance

In this regard Joule heating characteristics of freeze cast Ti3C2Tx MXene aerogels and

their composites with epoxy resin are investigated The morphological structural

electrical and thermal properties of those materials are examined The Joule heating

properties of the aerogels and their composites are measured in a custom-made setup

Steady-state measurement of the surface is performed to study reversibility and power-

temperature characteristics Finally rapid and repeatable temperature cycling of the

composites is demonstrated

62 Experimental section

621 Materials

Ti3AlC2 powders (purchased from Laizhou Kai Kai Ceramic Materials Co Ltd)

lithium fluoride (LiF purchased from Alfa Aesar) hydrochloric acid (HCl purchased

from Sigma Alrdrich) epoxy resin (Araldite LY5052) and the hardener (Aradur

HY5052 purchased from Huntsman) were used as obtained

622 Preparation of Ti3C2Tx

Ti3C2 MXenes were prepared by in-situ HF etching of Ti3AlC2 powders and the

experimental details can be found in our previous report[236] Briefly 3M LiF were

dissolved in 9 M HCl in high-density polyethylene (HDPE) container at room

temperature 2g of Ti3AlC2 powders were slowly added into the etching solution under

vigorous stirring The reaction was kept at 45 ordmC for 24 hours to etch the Ti3AlC2 The

etched MXenes were firstly washed with deionised water using a centrifuge (at 10K

rpm for 5 min per cycle) for multiple cycles to remove the excess acid In between

centrifuge cycles vigorous shaking by hand was applied to delaminate the etched

129

MXenes The delaminated MXenes were collected by collecting the supernatants from

multiple centrifuge cycles (at 35k rpm for 5 min per cycle) The delaminated MXenes

suspension was concentrated via centrifuge (at 10k for 1 hr) to obtain a stock suspension

which can later be used to prepare MXene suspensions for freeze casting

623 Preparation of 3D Epoxy resinTi3C2Tx MXene Aerogel composites

The MXene solution prepared above (120 mgcm3) was poured into a square PTFE

mould (with the dimension of 2 cm times 2 cm times 2 cm) and frozen by unidirectional freeze-

casting over a copper substrate Freeze-casting was conducted from 20 to -100 degC at a

cooling rate of 10 degCmin and the solid structure was then subsequently freeze-dried to

obtain a Ti3C2Tx aerogel To prepare the composite hardener was added to epoxy resin

(38 wt with respect to resin) and mixed by high shear mixing for 5 minutes The

mixture thereafter was kept in a vacuum oven for 10 minutes to remove any air bubbles

The Ti3C2Tx aerogel was immersed into the epoxy which was degassed and infiltrated

by vacuum-assisted infiltration for 1 h (Figure 61) After an initial 24thinsph curing step at

room temperature the samples were then post-cured at 100thinspdegC for 4thinsph in a conventional

oven

130


The cured sample was polished to remove the excess epoxy resin that was not infiltrated

into the aerogel to obtain the final epoxy resinTi3C2Tx MXene Aerogel composite The

mass loading of Ti3C2TX in the epoxy resinTi3C2Tx MXene Aerogel composite was

calculated by dividing the mass of the initial Ti3C2TX aerogel by the mass of the final

epoxy resinTi3C2Tx MXene Aerogel composite after polishing The final epoxy

resinTi3C2Tx MXene Aerogel composite was found to have 10 wt loading of

Ti3C2TX The photographic image of bare Ti3C2Tx MXene and epoxy resinTi3C2Tx

MXene Aerogel composite is shown in Figure 62 a and b respectively For comparison

Ti3C2TX epoxy composite with 10 wt loading of Ti3C2TX was prepared by dispersing

delaminated Ti3C2TX flakes in epoxy resin using a shear mixing method followed by

the same degassing and curing process

131



composite and (d) Ti3C2TX aerogel during the Joule heating




In the heating zone the temperature-time profile can be expressed by the following

equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)

where T0 Tm and Tt are the initial temperature maximum temperature and arbitrary

temperature at any time (t) respectively

The net heat gain is transferred to the surroundings by radiation and convection (hr+c)

in the heating zone was calculated via the following equation

132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)

To find out the characteristic decay time constant (120591119889) the cooling profile was fitted

with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)


The surface morphological images of the as-prepared samples were acquired by

scanning electron microscope (SEM Ultra-55 Germany) X-ray micro-computed

tomography (microCT) imaging was performed using a Zeiss Versa 520 (Zeiss Oberkochen

Germany) with the tube voltage of 60 kV and 5 W power in phase-contrast mode 3001

projections were taken at an exposure time of 12 s per projection Source to sample and

sample to detector distances were 260 and 435 mm respectively 4times magnification was

used and the voxel size was 1264 microm Data were reconstructed using XRM scout-and-

scan control system (Zeiss Oberkochen Germany) and visualised using Avizo (version

20193 Thermo Fisher Scientific Waltham MA US) Powder X-ray diffraction was

undertaken using a Proto AXRD θ-2θ diffractometer (284 mm diameter circle) with a

sample spinner and Dectris Mythen 1K (501deg active length) 1D-detector in Bragg-

Brentano geometry employing a Copper Line Focus X-ray tube with Ni Kβ absorber

(002 mm Kβ = 1392250 Å) Kα radiation (Kα1 = 1540598 Å Kα2 = 1544426 Å Kα

ratio 05 Kαav = 1541874 Å) at 600 W (30 kV 20 mA) X-ray photoelectron spectra

(XPS) measurements were performed by a PHI Quantera SXMAES 650 Auger

Electron Spectrometer (ULVAC-PHI Inc) equipped with a hemispherical electron



133

The electrical properties of epoxy resinTi3C2Tx MXene Aerogel composite have been

tested as the same method in section 326

63 Result and Discussion

631 Morphological analysis

The surface morphologies of Ti3C2Tx and its epoxy composite aerogels are shown in

Figure 63 a-b An anisotropic porous nature of the Ti3C2Tx aerogel with interconnected

MXene flakes is evidenced from Figure 63 b During the freeze-casting process

MXene flakes are excluded from the entrapped regions between the anisotropically

grown ice crystals As a result highly ordered layered assemblies of 3D porous MXene

aerogel are formed with uniform pores with an average size of around 45 microm Such

microstructure where each flake can serve as an nanoheater[185] may facilitate better

electrical and thermal transportation during the Joule heating process compared to their

randomly oriented counterparts[108] A jagged crack pattern and the rough surface of

the epoxyaerogel composite can be seen in Figure 63 c confirming the effective

infiltration of epoxy into the MXene aerogel


aerogel and (b) epoxy resinTi3C2TX MXene aerogel composite

The microCT image of epoxy resinTi3C2TX MXene aerogel composite is shown in Fig 64

134

The cross-section image (left) shows homogenous Mxene sheets domains across the

scanning area The region of interest has been picked up for creating the 3D image as

shown on the right A 3D lamellae structure of MXene is confirmed which serves as a

scaffold for the epoxy resinTi3C2TX MXene aerogel composite Within the microCT

scanned volume no air filled pores were visible which confirmed the excellent

infiltration of epoxy within the aerogel matrix



(middle and right) showing sheets oriented within a single domain Red vectors indicate

the freezing direction The Yellow dashed box indicates a region of interest

632 X-ray diffraction studies

To validate the successful synthesis of Ti3C2Tx XRD of all samples was recorded and

shown in Figure 65 (a) The (002) peak of Ti3C2Tx is found to have shifted towards a

smaller angle around 7deg and broadened compared to its MAX phase counterpart (~10 deg)

which certainly indicates a successful extraction of Al-atoms from Ti3AlC2 Moreover

the characteristic peaks between 33 and 43o of Ti3AlC2 have vanished for both of the

Ti3C2Tx samples These facts show that Ti3C2Tx was successfully synthesised by the in-

situ etching process It should be noted that the XRD spectra for delaminated Ti3C2Tx

135

and as-prepared Ti3C2Tx aerogel are similar indicating the excellent stability of Ti3C2Tx

flakes even after the freeze-casting method

633 Electrical conductivity

Increasing the resistive features of Ti3C2TX by incorporating epoxy is evidenced in

Figure 65 b The room temperature electrical conductivity for Ti3C2TX aerogelepoxy

is found to be 21 Scm at 1Hz which is lower than the bare Ti3C2TX aerogel (31 Scm)

and much higher than the epoxy resin (~10-11 Scm) The relative reduction in electrical

conductivity in the composite aerogel is due to the epoxy resin incorporation into the

aerogel separating the flakes slightly It is noteworthy that both the Ti3C2TX aerogel and

epoxy resinTi3C2TX MXene aerogel composite are quite independent with the applied

frequency and hence the resistive component dominates in this case The impedance of

the comparison sample where Ti3C2TX flakes were directly mixed into epoxy is also

shown (Figure 65 b) This sample was highly resistive[185] showing the importance

of the percolated connected nature of aerogel on imparting good electrical conductivity

136



Ti3C2Tx aerogel with respect to the (b) frequency and (c) temperature

137

The electrical conductivity of the Ti3C2TX aerogel was almost completely independent

of temperature whereas a drastic drop in conductivity occurred for the epoxy

resinTi3C2TX MXene aerogel composite (Figure 65 c) Note that the measurement of

electrical conductivity of the Ti3C2TX aerogel was restricted to 50 degC since MXenes are

very sensitive to temperature in ambient conditions due to the attached functional

groups In contrast to the Ti3C2TX aerogel the electrical conductivity of epoxy

resinTi3C2TX MXene aerogel is measured at a relatively high temperature to ensure the

stability and integrity of epoxy in the Ti3C2TX aerogel

634 X-ray photoelectron spectroscopic result

The X-ray photoelectron spectroscopic was employed to investigate the chemical

structure of Ti3C2TX aerogel and its epoxy composites The peak observed at 287thinspeV

531thinspeV and 685thinspeV was assigned to O1s C1s and F1s respectively [40] and the peak

at 35thinspeV 60thinspeV 457thinspeV and 563thinspeV was corresponded to the characteristic peaks of

Ti3p Ti 3s Ti 2p and Ti 2s respectively Thus both samples confirmed the presence

of main constituent elements of Ti3C2TX MXene and the terminated groups It is

noteworthy to mention that the epoxyTi3C2TX contains a higher amount of carbon and

oxygen than the bare Ti3C2TX MXene aerogel due to the epoxy resin

138


Ti3C2TX aerogel composite

Figure 67 High-resolution XPS of Ti2p C1s O1s and F1s peaks of epoxy

resinTi3C2TX MXene aerogel before Joule heating test

The high-resolution spectra of each element of epoxy resinTi3C2TX MXene aerogel are

139

deconvoluted by CASAXPS software after Shirley background subtraction Extracted

parameters of the fitted data are given in table 61 The Ti2p spectrum is deconvoluted

into six peaks corresponding to Ti atoms (4550 4558 and 4571 eV) TindashO (4587 eV)

TiO2-xFx (4593 eV) and CndashTindashFx (4602 eV) and this is consistent with the

literature[239] Since the peak around 282 eV in C1s spectra is asymmetric (Figure 67

c) and hence it is fitted with two symmetric peaks (C-Ti-Tx and carbide)[240] The O1s

peak is deconvoluted into five symmetrical peaks The fitting peaks around 5299 5316

5320 5325 and 5337 eV are attributed to Ti-O C-OH C-Ti-(OH)x C=O and O=C-

OH [239241] The results show that Ti3C2TX MXene and epoxy resin formed a hybrid

structure composite which is a good agreement with SEM and μCT images


Joule Heating test

Region BE (eV) FWHM

(eV)

Concentration Assigned to

Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140

5314 10 55 C-Ti-Ox andor OR

5318 19 55 C-Ti-(OH)x andor OR

533 2 37 Al2O3 andor OR

5341 11 19 H2Oads andor OR

5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x

635 Joule heating characteristion

The excellent Joule heating feature of the composite was validated by the IR image

inspection at different applied voltages (Figure 68 a-f) The steady-state temperature

of epoxy resinTi3C2TX aerogel composite was found to increase from 43 to 127 degC as

the applied voltage was increased from 1 to 2 V At 3 V applied voltage with 78 A

current the steady-state temperature of the composite was raised to 166 degC The

obtained result is impressive among the electrothermal materials reported in the

literature (Table 62) Our intention in table 62 is to show the importance of filling the

polymer into the 3D interconnected skeleton over the composite film such that the best

performance from the composite can be obtained Essentially 3D structures are well

known to offer excellent electrical and thermal conducting pathways[120] The steady-

state temperature of Ti3C2TX aerogelepoxy is higher than the bare Ti3C2TX aerogel at

the same input voltage which can be visualized from Figure 68 For instance at the

same input voltage of 2 V the Ti3C2TX aerogel surface can only heat up to 483 degC with

67 A current (Figure 68 i) whereas epoxy resinTi3C2TX aerogel composites with 51

141

A current can provide a much higher steady-state temperature of 123 degC Thermal IR

images of the Ti3C2TX aerogel at different voltages are shown in Figure 68 g-i The

Ti3C2TX MXene aerogel heater also outperforms the Ti3C2TX MXene thin film and

thread heater [233]

Figure 68 Steady-state thermal IR images of epoxy resinTi3C2TX aerogel composite

held at different input voltages of (a) 1 V (b) 125 V (c) 15V (d) 175V (e) 2V and (f)

3 V and Ti3C2TX aerogel at different voltage of (g) 1 V (h) 15 V and (i) 2 V

It should be noted that any rise in temperature is not observed from the epoxy

resinTi3C2TX MXene composite synthesized by simple shear mixing with any

application of external voltage up to 20 V As discussed before the Joule heating

performance of the samples always depends on its own electrical conductivities The

resinTi3C2TX MXene sample here showing very low electrical conductivities which

can not allow current flow going through the sample and generate the heat However a

few studies have reported the resinTi3C2TX MXene composite showing a relatively

high electrical conductivities compare with our samples with conventional method

142

[242] for example Wang et al [243] reported the resinTi3C2TX MXene composite

gives a ~2 Sm electrical conductivity value which is 7 orders higher than our samples

(~10-7 Sm) Such relatively high electrical conductive value may raise the potential for

Joule heating performance for samples This may because the mixing technique

difference between our methods and from others such as low mixing short mixing time

etc gives our sample a bad dispersion of MXene flakes in the epoxy resin system which

results in incomplete electrically conducting pathways However this still needs further

investigation to understand the full mechanism

Both rGOGNP aerogels in chapter 4 and MXene aerogels (chapter 6) are prepared both

with unidirectional freeze casting technique The epoxy resinTi3C2TX MXene aerogel

composites are also expected with different Joule heating properties in different

directions as discussed in section 434

Although Ti3C2TX has been found to be exhibit promising and impressive Joule heating

features[233][234] the combination of epoxy and Ti3C2TX aerogel is demonstrated as

a potential candidate due to better electrothermal behaviour

143


resinTi3C2TX MXene aerogel composite and (b) Ti3C2TX Mxene aerogel at an applied

voltage of 2V

Another prominent feature of thermal images of all samples is the spatial variation in

temperature over an approximate 13 times 13 cm2 area (Figure 68 and 69) It is

noteworthy that the central uniform part of the epoxy resinTi3C2TX MXene aerogel

composite is observed to be around 40 higher temperature relatively hotter than its

peripheral region (Figure 68 a-f and Figure 69 a) On the contrary non-uniform

temperature distribution over the surface has been observed from the Ti3C2TX aerogel

(Figure 69 a-b) In addition the central part shows a lower surface temperature than

the two sides of the bare Ti3C2TX aerogel This is due to the porosity of the Ti3C2TX

aerogel which allows heat convection and radiation to the surrounding air and the

thermally isolating nature of the air in the aerogel structure that restricts the heat

transfer[244] However at the sides of the sample lower air density and direct contact

with the clump at the sides of the sample give rise to a locally higher temperature field

144

(Figure 68 g-i) On the other hand epoxy resin is uniformly incorporated throughout

the Ti3C2TX aerogel and hence able to maintain the surface temperature quite uniformly

upon application of the external voltage

As seen from Figure 610 a the Joule heating profile of the sample follows three-stages

the initial increase in surface temperature with time (0 - 160 s) steady-state zone (160

- 800 s) and recovery regime to its original condition (800 - 1000 s) The rise in

temperature is directly proportional to the square of applied voltage and inversely

proportional to the resistance of materials It has also been seen that the electrical

conductivity reduces linearly with the temperature (Figure 65 c) Hence at a higher

applied voltage a better and quicker response in the temperature distribution is

observed for the epoxy resinTi3C2TX aerogel composite (Figure 610 b-c) The response

time which is defined as the time required to attain 90 of the steady-state temperature

from room temperature is another deciding factor for evaluating the Joule heating

performances (see Table 62) The composite shows a heating rate of 35 degCscm3 at

the initial stage under the applied voltage of 3 V (Figure 610 c) It is also important to

see from Figure 610 c that the cooling profile of the aerogel composite follows similar

trends with respect to the applied voltage like heating rate A greater dissipation takes

place at a higher temperature and it can maintain the steady-state temperature for the

desired time indicating its ldquoself-regulatingrdquo behaviour As a higher voltage is applied

the power delivery is increased and hence the surface temperature of epoxy

resinTi3C2TX aerogel composite is increased up to 166 degC at 3 V The drastic

enhancement of specific power (power density) from 17 to 139 Wcm2 (57 to 463

Wcm3 considering a height of 3 mm) is observed as the input voltage increased from

1 to 3V shown in Figure 610 d The energy density of the studied materials is estimated

using the relation specific energy = specific power times heating time (see Table 62) This

result confirms the significant benefits of using our composite as an effective heater

145


versus time of the epoxy resin Ti3C2TX MXene aerogel composite at different applied

voltages (c) Heating and cooling rate (solid line is guide to the eye only) and (d)

specific power of composite with respect to the applied voltage

To gain insight into the electric heating behaviour of the epoxy resin Ti3C2TX aerogel

composite the temperature-time profile (Fig 610 a) was further analysed In the

heating zone The temperature-time profile can be expressed according to equation 61

The characteristic rate constant (120591g) values for the composite could be evaluated by

fitting data in the heating zone of the temperature-time plots as summarized in Table

63 A low 120591g value represents a faster thermal response to the applied voltage It is

clearly seen from Figure 610 a that the surface temperature of the composite is higher

and found to be stable over 10 min without any deterioration at higher input voltage

(V0) and steady-state current (Ic) In this zone the net heat gain is transferred to the

surroundings by radiation and convection (hr+c) via the equation 62

146

As given in Table 63 this value of hr+c highlights the good electric heating efficiency

of the epoxy resinTi3C2TX MXene aerogel composite[237] In the cooling zone the

surface temperature of epoxy resinTi3C2TX MXene aerogel composite drops very

rapidly as the input voltage is turned off To find out the characteristic decay time

constant (120591119889) the cooling profile was fitted with Equation 63 and the extracted value

is tabulated (see Table 62)

Table 6-2 Extracted characteristic parameters (120591g 120591d and hr+c) for the Joule heating


Sample Voltage (V) 120649g (s) hr+c (W) 120649d (s)

epoxy

resinTi3C2Tx

aerogel

composite

1 387plusmn05 0050 280plusmn13

125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32


Ti3C2Tx aerogel 2 1022plusmn21 0348 244plusmn78

A low 120591119889 value at a higher applied voltage indicates faster recovery of the composite

Overall the composite shows a faster response with excellent heat dissipation along the

in-plane of MXene alignment Impressively the cooling profile of the composite is

found to be a mirror image of heating characteristics and are in good agreement with

Equation 61 and 63

147

Figure 611 (a) Prolonged steady-state phase and (b) Cycle test at the applied voltage

of 2 V of bare MXene aerogel and epoxy resin Ti3C2TX MXene aerogel composite (c)

cycle profile of temperature for the epoxy resin Ti3C2TX MXene aerogel composite at

different applied voltages

148

To examine the stability of the materials the Joule heating test was repeated for a

prolonged steady-state phase and several times at 2 V applied voltage Figure 611 a

shows the prolonged steady-state phase of bare MXene aerogel and epoxy resin

Ti3C2TX MXene aerogel composite for 4 hrs Moreover Figure 611 b shows the Joule

heating cycles of the epoxy resinTi3C2TX MXene aerogel composite and bare MXene

aerogel for several cycles at an applied voltage of 2 V The cycle stability of epoxy resin

Ti3C2TX aerogel composite at different applied voltages is shown in Fig 611 c for each

input voltage The temperature profile of bare MXene aerogel and epoxy resin Ti3C2TX

MXene aerogel composite for repeated cycles is shown in Fig 612


epoxy resin Ti3C2TX MXene aerogel composite

The trapped water molecules between MXene layers could be evaporated during the

rapid local heating leading to crack formation and hence it may lead to performance

deterioration Since we cured the composite at the temperature of 100 degC over a long

time of 4 hrs such kinds of possibilities are ignored here Most importantly the

obtained results from Fig 69 are direct proof of the structural stability of the aerogel

composite as an electrothermal heater To strengthen the statement we carried out XPS

study of the studied materials after Joule heating performances (Fig 613) The XPS

result of the aerogel composite before the Joule heating is shown in Fig 66 and Fig

67 The extracted elemental composition is listed in Table 64 As seen from Table 64

149

epoxy resin Ti3C2TX MXene aerogel composite does not show any significant

structural changes However slight changes in the TiC ratio from 129 to 153 have

been observed for the bare Ti3C2TX MXene after the Joule heating (Table 63) This

change can be attributed to the formation of TiO2 on the surface It is important to note

that TiC ratio of epoxy resin Ti3C2TX MXene is relatively lower than the epoxy due

to the carbon content of the epoxy Although the epoxy resin Ti3C2TX MXene aerogel

composite reaches a much higher surface temperature compared to the bare MXene

aerogel the existing epoxy resin can protect the MXene nanofillers in the composites

from oxidation and hence the TiC ratio is remains unchanged even after Joule heating

Thus our result confirms that both MXene aerogel and epoxy resin Ti3C2TX MXene

aerogel composite have excellent structural stability even after several Joule heating

cycles and after prolonged steady-state thermal exposure


and epoxy resin Ti3C2TX MXene aerogel composite

Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion

This chapter demonstrates an efficient strategy for preparing an epoxy resinTi3C2Tx

150

MXene aerogel composite via the infiltration of epoxy into the MXene aerogel A high-

efficiency energy conversion rapid heatingcooling rate and excellent stability for

longer cycles are confirmed from the Joule heating performance of the epoxy

resinTi3C2TX Mxene aerogel composite Importantly the fabricated aerogel composite

has shown a more effective Joule heating feature with three-time higher steady-state

temperature than bare MXene aerogel at the same applied voltage The excellent Joule

heating performance of the composite is attributed to the synergistic effect of MXene

and epoxy resin along with their three-dimensional structure On the other hand

reinforced epoxy resin replacing the air from MXene aerogel serves as an excellent

mediator to dissipate the heat along the direction of MXene sheet alignment and a

protector for MXene from its oxidation This novel approach to prepare 3D composites

paves the way towards the fabrication of electrothermal heaters to be used for energy-

efficient de-icing and other thermal management applications

151

7 Chapter 7 Conclusions and Future Work

71 Conclusions

In this thesis the simple and scalable route to fabricate epoxy2D materials-based

aerogel composite has been demonstrated successfully

Firstly 3D structures of 2D materials were architectured and the intrinsic properties

including electrical thermal mechanical and hence Joule heating was tuned in a

controlled manner and the final structure was utilized as a scaffold to prepare the

epoxyaerogel composites The key outcomes of the thesis chapter-wise are concluded

as below

1 rGO-GNP hybrid lamellar architectures by combining partial chemical reduction

and unidirectional freeze-casting followed by a final heat treatment step have been

demonstrated The effective stabilizability of GNP in aqueous dispersions by both

GO and rGO has been proven by zeta potential characterization The Raman and

XPS techniques results indicate the successful reduction and removal of functional

groups from the GO surface By optimized the chemical reduction time and the

benefit from non-oxidized graphene materials (GNP) the CR35TR300 samples with

optimized chemical reduction time of 35 minutes only exhibited the highest

compressive modulus (051 plusmn 006 Mpa and strength of 0028 plusmn 00026 Mpa)

amongst all the samples with great recoverability after a large strain of 35 On the

other hand CR60TR300 samples (chemical reduction for 60 minutes) exhibited the

highest electrical conductivity of 423 Sm and a water contact angle of 1068 ordm

2 The rGOGNP aerogel with the highest GNP content showed the highest electrical

thermal and mechanical properties Compare with the conventional sheer mixing

technique this aerogel is proven as an efficient filler network for the epoxy

composite and showed a 9 orders higher electrical conductivity It has been shown

that the Joule heating-induced steady-state temperature of the final aerogel

composite is linearly related to their electrical and thermal conductivities The best

aerogel composite showed an excellent Joule heating performance with a steady-

152

state temperature of 213 degC at a relatively low applied voltage of 5V and excellent

cycle life The mechanical properties of composites were tested by flexural and

Model I fracture toughness tests The composites showed around 287 654

and 814 improvement for their flexural strength flexural modulus and stress

intensity factor (K1c) respectively

3 To explore the concept of 3D graphene aerogel reinforced polymer composites for

traditional carbon fabrics GO aerogel (GOA) interpenetrated-carbon fibre epoxy

composites have been successfully developed The SEM results confirmed the

uniform porous 3D graphene-carbon fiber structure The Model I fracture toughness

results exhibit the GOA interpenetrated-carbon fibre epoxy composites showed a

significant enhancement in both K1c and G1c compared with pure carbon fiber epoxy

composites This enhancement is contributed by both uniform graphene dispersion

leading to significant deflectionmicrocracking in the matrix and aligned graphene

structure Moreover the 3D anisotropic graphene structure provides more electrical

path for electric transfers through composites for both in-plane and out-of-plane

direction thus dramatically increased electrical conductivity

4 Later another 2D material Ti3C2Tx MXene has been synthesized successfully by

in-situ etching method and the aerogel was prepared by the freeze-casting method

MXene aerogel was found to be an excellent mechanical backbone for the epoxy

composite and showed excellent Joule heating performances The epoxy resin

Ti3C2Tx MXene aerogel composite showing an electrical conductivity of 21 Sm A

steady-state temperature of 123 degC was obtained by applying a low voltage of 2 V

with 51 A current giving a total power output of 61 Wcm2 with repeated heating-

cooling cycles have been obtained from the Joule heating test Moreover XPS

results indicated both MXene aerogel and MXene aerogel based epoxy composites

showed excellent structural stability even after a long-term and repeated (100 cycles)

Joule heating test

5 A comparison between graphene aerogel-based epoxy composites and MXene

aerogel-based epoxy composites has been summarised in Table 71 below In this

153

thesis the filler loading in MXeneepoxy aerogel composite is more than twice as

graphene-based aerogel composites such a high loading of fillers gives

MXeneepoxy aerogel composite a much higher electrical conductivity when

compared to graphene-based aerogel composites which allow current flow in

MXeneepoxy aerogel composite (51 A) is around 7 times higher than the current

flow in graphene-based aerogel composites (065 A) with the same power input (3

V) Thus the overall Joule heating performance of MXeneepoxy aerogel composite

such as steady-state surface temperature and the heating rate is better than graphene-

based aerogel composites However to further understand the reason some other

tests for example the heat capacity difference between graphene and MXene needs

to be done But due to the time limits such experiments have not been performed

here


composites and MXene aerogel epoxy composites

Sample rGOGNP aerogel

based epoxy

composites

MXene aerogel based

epoxy composites

Fillers loading (wt) 46 10

Electrical conductivities (Scm) 05 21

Voltage input (V) 3 3

Current (A) 065 51

Power density (Wcm3) 102 463

Steady-state surface

temperature (degC)

134 166

Heating rate (degCmin) 574 623

Cooling rate (degCmin) 556 611

6 A comparison between epoxy resingraphene-based aerogel composites with

reported electrothermal materials has been summarised om Table 72 below In this

thesis epoxygraphene-based composites showing overall better Joule heating

154

performance than epoxygraphene-based composites prepared with the

conventional method for example the EpoxyGNR composites needs around 500

seconds to reach their steady-state temperature which is more than 3 times longer

than the EGAC-10 samples Moreover the EGAC-10 showing a higher steady-state

temperature of 213 degC compare with EpoxyGNR samples It can be obtained that

EGAC-10 samples showing slower response time and lower heating rate compare

with aerogels samples such as BNrCNT and BNrGO aerogels However due to

the better thermal conductivity of EGAC-10 samples the steady-state temperature

is almost twice higher as aerogel-based materials


reported electrothermal materials (l length b breadth and h height)

Materials

(l cm times b cm times h cm)

Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based

aerogel composite EGAC-

10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102

3D graphene foamPDMS

(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites

(10times10times03) [248]

~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS

composites (~) [249]

6 ~100 840 71 ~

(rGO reduced Graphene Oxide rCNT Reduced Carbon Nanotube PEEK Poly ether

ether ketone PDMS polydimethylsiloxane GNR Graphene nanoribbon)

values are calculated based on the data available in the respected references

155

7 A comparison between epoxy resin Ti3C2TX MXene-based aerogel composites with

reported electrothermal materials has been summarised om Table 73 below The

epoxy resin Ti3C2TX MXene-based aerogel composites showing better Joule

heating performance in terms of heating rate steady-state temperature response

time etc than graphene-based polymer composites with less than 10 V power input

There are some materials from the literature showing similar Joule heating

performance compare with our epoxy resin Ti3C2TX MXene-based aerogel

composites however it requires a much higher power input for example the

rGOEpoxy film needs 30 V power input which is 10 times higher than the power

we used here The traditional metal-based materials showing a 75 Wcm2 power

density which is almost 10 times higher than epoxy resin Ti3C2TX MXene-based

aerogel composites However such high power density does not contribute to its

other Joule heating properties such as heating rate steady-state temperature and

response time and all showing a lower value than our MXene aerogel-based epoxy

composites It should be noted that rGO film showing a greater response time of 10

sec heating rate of 810 degCmin due to its high electrical conductivity



and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100

Epoxy Ti3C2TX aerogel

(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -

Graphene-coated glass

rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -

(MMT montmorillonite PPy Polypyrrole GNP Graphene NanoPlatelets rGO

reduced Graphene Oxide MWCNT Multi-walled Carbon Nanotube GNR Graphene

nanoribbon PDMS polydimethylsiloxane)


The concept of designing 3D aerogel polymer composite with multifunctionality shown

in this thesis could open a new opportunity to improve the electrical conductivity

thermal conductivity fracture toughness and can be used as its potential applications

for sports automotive aerospace industries and other thermal management

72 Future work

The manufacturing of GOGNP suspension (Chapter 3) was a good starting for

investigating GO dispersibility for graphene-based 2D materials The study can be

extended with other 2D materials such as MXene h-BN MoS2 etc Moreover for the

157

freeze-casting technique more parameters such as freeze rate the final cooling

temperature can be investigated to understand the influence of the final aerogel

structure electrical conductivity and mechanical response In addition to that the

compressive test for rGOGNP aerogel result indicates the outstanding elastic property

However serval studies showed that the electrical conductivity has a significant

correlation with the compressive strain of graphene-based aerogel Hence to explore

the full potential of rGOGNP aerogel for sensing applications the electrical

conductivity measurement with compressive test needs to be carried out in the future

In Chapter 4 the influence of mechanical property electrical conductivity thermal

conductivity and Joule heating property of GNP content for rGOGNP aerogel epoxy

composites has been studied However to explore the rGOGNP aerogel epoxy

composites for deicing applications more parameters need to be considered and studied

for the deicing test such as the thickness of ice atmosphere temperature atmosphere

humidity

In Chapter 5 the GO aerogel reinforced carbon fiber epoxy composites have been

successfully developed The final composites showed a significant improvement for its

Model I fracture toughness and electrical conductivity However the influence of GO

content on the composites has not been studied yet Moreover the freezing conditions

and directions can also be deciding factors and hence further study to understand the

influence of microstructure mechanical property and electrical conductivity will be

well-appreciated

In Chapter 6 high-efficiency MXene aerogelepoxy composites for Joule heating

applications have been demonstrated However more deicing tests need to be

considered to explore the full potential for deicing applications as well as the fluence

of MXene content and freeze casting conditions that need to be studied In terms of

characterization of MXene aerogel-based epoxy composites although it showed great

electrical conductivity and Joule heating performance the mechanical properties need

to be experimentally determined

158

References

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[3] Wang R M Zheng S R and Zheng Y P 2011 Polymer matrix composites and

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[4] Wei J Saharudin M S Vo T and Inam F 2017 NN-Dimethylformamide

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[5] Hodgkin J H Simon G P and Varley R J 1998 Thermoplastic toughening of

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[7] K S Novoselov A K Geim S V Morozov D Jiang Y Zhang S V

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[9] Yuan S Pang S Y and Hao J 2020 2D transition metal dichalcogenides

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[11] Cui X Zhang C Hao R and Hou Y 2011 Liquid-phase exfoliation

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[13] Stankovich S Dikin D A Dommett G H B Kohlhaas K M Zimney E J Stach

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[17] Li D Muumlller M B Gilje S Kaner R B and Wallace G G 2008 Processable

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[19] Hu M Hu T Li Z Yang Y Cheng R Yang J Cui C and Wang X 2018

Surface Functional Groups and Interlayer Water Determine the

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[20] Seh Z W Fredrickson K D Anasori B Kibsgaard J Strickler A L Lukatskaya

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M R Gogotsi Y Jaramillo T F and Vojvodic A 2016 Two-Dimensional

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[21] Ma T Y Cao J L Jaroniec M and Qiao S Z 2016 Interacting carbon nitride

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[22] Zhao Y Watanabe K and Hashimoto K 2012 Self-supporting oxygen

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[23] Ghidiu M Lukatskaya M R Zhao M Q Gogotsi Y and Barsoum M W 2015

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capacitance Nature 516 78ndash81

[24] Khazaei M Arai M Sasaki T Estili M and Sakka Y 2014 Two-dimensional

molybdenum carbides Potential thermoelectric materials of the MXene family

Phys Chem Chem Phys 16 7841ndash9

[25] Naguib M Mochalin V N Barsoum M W and Gogotsi Y 2014 25th

anniversary article MXenes A new family of two-dimensional materials Adv

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[26] Abel M Clair S Ourdjini O Mossoyan M and Porte L 2011 Single layer of

polymeric Fe-phthalocyanine An organometallic sheet on metal and thin

insulating film J Am Chem Soc 133 1203ndash5

[27] Chaudhari N K Jin H Kim B San Baek D Joo S H and Lee K 2017 MXene

An emerging two-dimensional material for future energy conversion and

storage applications J Mater Chem A 5 24564ndash79

[28] Tontini G Greaves M Ghosh S Bayram V and Barg S 2020 MXene-based

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[29] Jorfi M and Foster E J 2015 Recent advances in nanocellulose for biomedical

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[30] Ling C Shi L Ouyang Y Chen Q and Wang J 2016 Transition Metal-

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[31] Ghidiu M Halim J Kota S Bish D Gogotsi Y and Barsoum M W 2016 Ion-

Exchange and Cation Solvation Reactions in Ti3C2 MXene Chem Mater 28

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[32] Potts J R Dreyer D R Bielawski C W and Ruoff R S 2011 Graphene-based

polymer nanocomposites Polymer (Guildf) 52 5ndash25

[33] Wang X Tan D Chu Z Chen L Chen X Zhao J and Chen G 2016

Mechanical properties of polymer composites reinforced by functionalized

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[34] Huo C Yan Z Song X and Zeng H 2015 2D materials via liquid exfoliation a

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[36] Geim A K 2009 Graphene Status and prospects Science (80- ) 324 1530ndash4

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[43] Chen Z Dai X J Magniez K Lamb P R Rubin De Celis Leal D Fox B L and

Wang X 2013 Improving the mechanical properties of epoxy using multiwalled

carbon nanotubes functionalized by a novel plasma treatment Compos Part A

Appl Sci Manuf 45 145ndash52

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[46] Wei J Atif R Vo T and Inam F 2015 Graphene Nanoplatelets in Epoxy

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[47] Tang L C Wan Y J Yan D Pei Y B Zhao L Li Y B Wu L Bin Jiang J X

and Lai G Q 2013 The effect of graphene dispersion on the mechanical

properties of grapheneepoxy composites Carbon N Y 60 16ndash27

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technologies Sol Energy Mater Sol Cells 144 559ndash78

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M S 2003 Structure and electrochemical properties of carbon aerogels

polymerized in the presence of Cu2+ J Non Cryst Solids 330 99ndash105

[51] Wang Z Shen X Han N M Liu X Wu Y Ye W and Kim J K 2016 Ultralow

Electrical Percolation in Graphene AerogelEpoxy Composites Chem Mater

28 6731ndash41

[52] Wang Z Shen X Akbari Garakani M Lin X Wu Y Liu X Sun X and Kim J

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structure and properties ACS Appl Mater Interfaces 7 5538ndash49

[53] Li X H Liu P Li X An F Min P Liao K N and Yu Z Z 2018 Vertically

aligned ultralight and highly compressive all-graphitized graphene aerogels for

highly thermally conductive polymer composites Carbon N Y 140 624ndash33

[54] Zhang D Zhang X Chen Y Yu P Wang C and Ma Y 2011 Enhanced

capacitance and rate capability of graphenepolypyrrole composite as electrode

material for supercapacitors J Power Sources 196 5990ndash6

[55] Wang Y Shi Z Huang Y Ma Y Wang C Chen M and Chen Y 2009

Supercapacitor devices based on graphene materials J Phys Chem C 113

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[56] Yin S Niu Z and Chen X 2012 Assembly of graphene sheets into 3D

macroscopic structures Small 8 2458ndash63

[57] Xu R Lu Y Jiang C Chen J Mao P Gao G Zhang L and Wu S 2014 Facile

fabrication of three-dimensional graphene foam poly(dimethylsiloxane)

composites and their potential application as strain sensor ACS Appl Mater

Interfaces 6 13455ndash60

[58] Zhu C Han T Y J Duoss E B Golobic A M Kuntz J D Spadaccini C M and

Worsley M A 2015 Highly compressible 3D periodic graphene aerogel

microlattices Nat Commun 6

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MXene-Based Fireproof Electromagnetic Shielding Films with Exceptional

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Appl Mater Interfaces 12 27350ndash60

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one-step hydrothermal process ACS Nano 4 4324ndash30

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2012 Low temperature casting of graphene with high compressive strength

Adv Mater 24 5124ndash9

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graphene oxide Chem Soc Rev 39 228ndash40

[63] Kim F Cote L J and Huang J 2010 Graphene oxide Surface activity and two-

dimensional assembly Adv Mater 22 1954ndash8

[64] Kim J Cote L J Kim F Yuan W Shull K R and Huang J 2010 Graphene

oxide sheets at interfaces J Am Chem Soc 132 8180ndash6

[65] Vickery J L Patil A J and Mann S 2009 Fabrication of graphene-polymer

nanocomposites with higher-order three-dimensional architectures Adv Mater

21 2180ndash4

[66] Bai H Sheng K Zhang P Li C and Shi G 2011 Graphene oxideconducting

polymer composite hydrogels J Mater Chem 21 18653ndash8

[67] Zu S Z and Han B H 2009 Aqueous dispersion of graphene sheets stabilized

by pluronic copolymersFormation of supramolecular hydrogel J Phys Chem

C 113 13651ndash7

[68] Zhang Y Z El-Demellawi J K Jiang Q Ge G Liang H Lee K Dong X and

Alshareef H N 2020 MXene hydrogels Fundamentals and applications Chem

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[69] Wu Z S Yang S Sun Y Parvez K Feng X and Muumlllen K 2012 3D nitrogen-

doped graphene aerogel-supported Fe 3O 4 nanoparticles as efficient

electrocatalysts for the oxygen reduction reaction J Am Chem Soc 134 9082ndash

5

[70] Hou Y Li J Wen Z Cui S Yuan C and Chen J 2014 N-doped

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165

anode materials for lithium-ion batteries Nano Energy 8 157ndash64

[71] Worsley M A Pham T T Yan A Shin S J Lee J R I Bagge-Hansen M

Mickelson W and Zettl A 2014 Synthesis and characterization of highly

crystalline graphene aerogels ACS Nano 8 11013ndash22

[72] Eda G Fanchini G and Chhowalla M 2008 Large-area ultrathin films of

reduced graphene oxide as a transparent and flexible electronic material Nat

Nanotechnol 3 270ndash4

[73] Wang X Zhi L and Muumlllen K 2008 Transparent conductive graphene

electrodes for dye-sensitized solar cells Nano Lett 8 323ndash7

[74] Nguyen S T Nguyen H T Rinaldi A Nguyen N P V Fan Z and Duong H M

2012 Morphology control and thermal stability of binderless-graphene aerogels

from graphite for energy storage applications Colloids Surfaces A

Physicochem Eng Asp 414 352ndash8

[75] Li J Wang F and Liu C yan 2012 Tri-isocyanate reinforced graphene aerogel

and its use for crude oil adsorption J Colloid Interface Sci 382 13ndash6

[76] Wu Y Yi N Huang L Zhang T Fang S Chang H Li N Oh J Lee J A

Kozlov M Chipara A C Terrones H Xiao P Long G Huang Y Zhang F

Zhang L Leproacute X Haines C Lima M D Lopez N P Rajukumar L P Elias A

L Feng S Kim S J Narayanan N T Ajayan P M Terrones M Aliev A Chu P

Zhang Z Baughman R H and Chen Y 2015 Three-dimensionally bonded

spongy graphene material with super compressive elasticity and near-zero

Poissonrsquos ratio Nat Commun 6

[77] Tang Z Shen S Zhuang J and Wang X 2010 Noble-metal-promoted three-

dimensional macroassembly of single-layered graphene oxide Angew Chemie -

Int Ed 49 4603ndash7

[78] Jiang X Ma Y Li J Fan Q and Huang W 2010 Self-Assembly of Reduced

Graphene Oxide into Three-Dimensional Architecture by Divalent Ion Linkage

J Phys Chem C 114 22462ndash5

[79] Tang M Wu T Na H Zhang S Li X and Pang X 2015 Fabrication of

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graphene oxide aerogels loaded with catalytic AuPd nanoparticles Mater Res

Bull 63 248ndash52

[80] Ren L Hui K N Hui K S Liu Y Qi X Zhong J Du Y and Yang J 2015 3D

hierarchical porous graphene aerogel with tunable meso-pores on graphene

nanosheets for high-performance energy storage Sci Rep 5

[81] Ren L Hui K S and Hui K N 2013 Self-assembled free-standing three-

dimensional nickel nanoparticlegraphene aerogel for direct ethanol fuel cells J

Mater Chem A 1 5689ndash94

[82] Wu X Zhou J Xing W Wang G Cui H Zhuo S Xue Q Yan Z and Qiao S Z

2012 High-rate capacitive performance of graphene aerogel with a superhigh

CO molar ratio J Mater Chem 22 23186ndash93

[83] Wu Z S Sun Y Tan Y Z Yang S Feng X and Muumlllen K 2012 Three-

dimensional graphene-based macro- and mesoporous frameworks for high-

performance electrochemical capacitive energy storage J Am Chem Soc 134

19532ndash5

[84] Wu Z S Ren W Xu L Li F and Cheng H M 2011 Doped graphene sheets as

anode materials with superhigh rate and large capacity for lithium ion batteries

ACS Nano vol 5 pp 5463ndash71

[85] Chen M Zhang C Li X Zhang L Ma Y Zhang L Xu X Xia F Wang W and

Gao J 2013 A one-step method for reduction and self-assembling of graphene

oxide into reduced graphene oxide aerogels J Mater Chem A 1 2869ndash77

[86] Li J Meng H Xie S Zhang B Li J Li L Ma H Zhang J and Yu M 2014

Ultra-light compressible and fire-resistant graphene aerogel as a highly

efficient and recyclable absorbent for organic liquids J Mater Chem A 2

2934ndash41

[87] Moon I K Yoon S Chun K Y and Oh J 2015 Highly Elastic and Conductive

N-Doped Monolithic Graphene Aerogels for Multifunctional Applications Adv

Funct Mater 25 6976ndash84

[88] Sui Z Y Meng Y N Xiao P W Zhao Z Q Wei Z X and Han B H 2015

167

Nitrogen-doped graphene aerogels as efficient supercapacitor electrodes and

gas adsorbents ACS Appl Mater Interfaces 7 1431ndash8

[89] Sui Z Y Wang C Shu K Yang Q S Ge Y Wallace G G and Han B H 2015

Manganese dioxide-anchored three-dimensional nitrogen-doped graphene

hybrid aerogels as excellent anode materials for lithium ion batteries J Mater

Chem A 3 10403ndash12

[90] Sui Z Y Wang C Yang Q S Shu K Liu Y W Han B H and Wallace G G

2015 A highly nitrogen-doped porous graphene - An anode material for lithium

ion batteries J Mater Chem A 3 18229ndash37

[91] Fang Q and Chen B 2014 Self-assembly of graphene oxide aerogels by

layered double hydroxides cross-linking and their application in water

purification J Mater Chem A 2 8941ndash51

[92] Lee W S V Peng E Choy D C and Xue J M 2015 Mechanically robust

glucose strutted graphene aerogel paper as a flexible electrode J Mater Chem

A 3 19144ndash7

[93] Lee J Stein I Y Kessler S S and Wardle B L 2015 Aligned carbon nanotube

film enables thermally induced state transformations in layered polymeric

materials ACS Appl Mater Interfaces 7 8900ndash5

[94] Sheng K X Xu Y X Li C and Shi G Q 2011 High-performance self-

assembled graphene hydrogels prepared by chemical reduction of graphene

oxide Xinxing Tan CailiaoNew Carbon Mater 26 9ndash15

[95] Pei S Zhao J Du J Ren W and Cheng H M 2010 Direct reduction of

graphene oxide films into highly conductive and flexible graphene films by

hydrohalic acids Carbon N Y 48 4466ndash74

[96] Moon I K Lee J Ruoff R S and Lee H 2010 Reduced graphene oxide by

chemical graphitization Nat Commun 1

[97] Park S An J Potts J R Velamakanni A Murali S and Ruoff R S 2011

Hydrazine-reduction of graphite- and graphene oxide Carbon N Y 49 3019ndash23

[98] Zhang X Sui Z Xu B Yue S Luo Y Zhan W and Liu B 2011 Mechanically

168

strong and highly conductive graphene aerogel and its use as electrodes for

electrochemical power sources J Mater Chem 21 6494ndash7

[99] Worsley M A Kucheyev S O Mason H E Merrill M D Mayer B P Lewicki

J Valdez C A Suss M E Stadermann M Pauzauskie P J Satcher J H Biener J

and Baumann T F 2012 Mechanically robust 3D graphene macroassembly with

high surface area Chem Commun 48 8428ndash30

[100] Zhang L Chen G Hedhili M N Zhang H and Wang P 2012 Three-

dimensional assemblies of graphene prepared by a novel chemical reduction-

induced self-assembly method Nanoscale 4 7038ndash45

[101] Tang H Gao P Bao Z Zhou B Shen J Mei Y and Wu G 2015 Conductive

resilient graphene aerogel via magnesiothermic reduction of graphene oxide

assemblies Nano Res 8 1710ndash7

[102] Deville S 2013 Ice-templating freeze casting Beyond materials processing J

Mater Res 28 2202ndash19

[103] Xie X Zhou Y Bi H Yin K Wan S and Sun L 2013 Large-range control of

the microstructures and properties of three-dimensional porous graphene Sci

Rep 3

[104] Ni N Barg S Garcia-Tunon E MacUl Perez F Miranda M Lu C Mattevi C

and Saiz E 2015 Understanding Mechanical Response of Elastomeric Graphene

Networks Sci Rep 5 1ndash14



Networks Sci Rep 5

[106] Wang C Chen X Wang B Huang M Wang B Jiang Y and Ruoff R S 2018

Freeze-Casting Produces a Graphene Oxide Aerogel with a Radial and

Centrosymmetric Structure ACS Nano 12 5816ndash25

[107] Bayram V Ghidiu M Byun J J Rawson S D Yang P McDonald S A

Lindley M Fairclough S Haigh S J Withers P J Barsoum M W Kinloch I A

and Barg S 2020 MXene Tunable Lamellae Architectures for Supercapacitor

169

Electrodes ACS Appl Energy Mater 3 411ndash22

[108] Bian R He G Zhi W Xiang S Wang T and Cai D 2019 Ultralight MXene-

based aerogels with high electromagnetic interference shielding performance J

Mater Chem C 7 474ndash8

[109] Ju M Yang Y Zhao J Yin X Wu Y and Que W 2020 Macroporous 3D

MXene architecture for solar-driven interfacial water evaporation J Adv

Dielectr

[110] Idowu A Boesl B and Agarwal A 2018 3D graphene foam-reinforced

polymer composites ndash A review Carbon N Y 135 52ndash71

[111] Embrey L Nautiyal P Loganathan A Idowu A Boesl B and Agarwal A 2017

Three-Dimensional Graphene Foam Induces Multifunctionality in Epoxy

Nanocomposites by Simultaneous Improvement in Mechanical Thermal and

Electrical Properties ACS Appl Mater Interfaces 9 39717ndash27

[112] Han N M Wang Z Shen X Wu Y Liu X Zheng Q Kim T H Yang J and

Kim J K 2018 Graphene Size-Dependent Multifunctional Properties of

Unidirectional Graphene AerogelEpoxy Nanocomposites ACS Appl Mater


[113] Kim J Han N M Kim J Lee J Kim J K and Jeon S 2018 Highly Conductive

and Fracture-Resistant Epoxy Composite Based on Non-oxidized Graphene

Flake Aerogel ACS Appl Mater Interfaces 10 37507ndash16

[114] Pettes M T Ji H Ruoff R S and Shi L 2012 Thermal transport in three-

dimensional foam architectures of few-layer graphene and ultrathin graphite

Nano Lett 12 2959ndash64

[115] Li M Sun Y Xiao H Hu X and Yue Y 2015 High temperature dependence of

thermal transport in graphene foam Nanotechnology 26

[116] Zhang X Yeung K K Gao Z Li J Sun H Xu H Zhang K Zhang M Chen Z

Yuen M M F and Yang S 2014 Exceptional thermal interface properties of a

three-dimensional graphene foam Carbon N Y 66 201ndash9

[117] Zhang K Yuen M M F Wang N Miao J Y Xiao D G W and Fan H B 2006

170

Thermal interface material with aligned CNT and its application in HB-LED

packaging Proceedings - Electronic Components and Technology Conference

vol 2006 pp 177ndash82

[118] Zhao Y H Zhang Y F and Bai S L 2016 High thermal conductivity of flexible

polymer composites due to synergistic effect of multilayer graphene flakes and

graphene foam Compos Part A Appl Sci Manuf 85 148ndash55

[119] Yao Y Sun J Zeng X Sun R Xu J Bin and Wong C P 2018 Construction of

3D Skeleton for Polymer Composites Achieving a High Thermal Conductivity

Small 14

[120] Bustillos J Zhang C Boesl B and Agarwal A 2018 Three-Dimensional

Graphene Foam-Polymer Composite with Superior Deicing Efficiency and

Strength ACS Appl Mater Interfaces 10 5022ndash9

[121] Jia J Du X Chen C Sun X Mai Y W and Kim J K 2015 3D network

graphene interlayer for excellent interlaminar toughness and strength in fiber

reinforced composites Carbon N Y 95 978ndash86

[122] Reddy S K Ferry D B and Misra A 2014 Highly compressible behavior of

polymer mediated three-dimensional network of graphene foam RSC Adv 4

50074ndash80

[123] Zhang Q Xu X Li H Xiong G Hu H and Fisher T S 2015 Mechanically

robust honeycomb graphene aerogel multifunctional polymer composites

Carbon N Y 93 659ndash70

[124] Jia J Sun X Lin X Shen X Mai Y W and Kim J K 2014 Exceptional

electrical conductivity and fracture resistance of 3D interconnected graphene

foamepoxy composites ACS Nano 8 5774ndash83

[125] Qiu Y Liu J Lu Y Zhang R Cao W and Hu P 2016 Hierarchical Assembly

of Tungsten Spheres and Epoxy Composites in Three-Dimensional Graphene

Foam and Its Enhanced Acoustic Performance as a Backing Material ACS


[126] Nautiyal P Boesl B and Agarwal A 2017 Harnessing Three Dimensional

171

Anatomy of Graphene Foam to Induce Superior Damping in Hierarchical

Polyimide Nanostructures Small 13

[127] Nieto A Dua R Zhang C Boesl B Ramaswamy S and Agarwal A 2015

Three Dimensional Graphene FoamPolymer Hybrid as a High Strength

Biocompatible Scaffold Adv Funct Mater 25 3916ndash24

[128] Liu J Wang T Wang J and Wang E 2015 Mussel-inspired biopolymer

modified 3D graphene foam for enzyme immobilization and high performance

biosensor Electrochim Acta 161 17ndash22

[129] Chen Z Xu C Ma C Ren W and Cheng H M 2013 Lightweight and flexible

graphene foam composites for high-performance electromagnetic interference

shielding Adv Mater 25 1296ndash300

[130] Chabi S Peng C Yang Z Xia Y and Zhu Y 2015 Three dimensional (3D)

flexible graphene foampolypyrrole composite Towards highly efficient

supercapacitors RSC Adv 5 3999ndash4008

[131] Zhao Y H Wu Z K and Bai S L 2016 Thermal resistance measurement of 3D

graphene foampolymer composite by laser flash analysis Int J Heat Mass

Transf 101 470ndash5

[132] Tembei S A Hessein A Fath El-Bab A M and El-Moneim A A 2020 A low

voltage flexible graphene-based electrothermal heater for wearable electronics

and localized heating applications Mater Today Proc

[133] Aouraghe M A Xu F Liu X and Qiu Y 2019 Flexible quickly responsive and

highly efficient E-heating carbon nanotube film Compos Sci Technol 183

[134] Qian Y Ismail I M and Stein A 2014 Ultralight high-surface-area

multifunctional graphene-based aerogels from self-assembly of graphene oxide

and resol Carbon N Y 68 221ndash31

[135] Gorgolis G and Galiotis C 2017 Graphene aerogels A review 2D Mater 4

[136] Gurunathan S Han J W Eppakayala V Dayem A A Kwon D N and Kim J H

2013 Biocompatibility effects of biologically synthesized graphene in primary

mouse embryonic fibroblast cells Nanoscale Res Lett 8 1ndash13

172

[137] Wang F Han L Zhang Z Fang X Shi J and Ma W 2012 Surfactant-free ionic

liquid-based nanofluids with remarkable thermal conductivity enhancement at

very low loading of graphene Nanoscale Res Lett 7

[138] Xie H Yu W Li Y and Chen L 2011 Discussion on the thermal conductivity

enhancement of nanofluids Nanoscale Res Lett 6

[139] Baby T T and Ramaprabhu S 2011 Enhanced convective heat transfer using

graphene dispersed nanofluids Nanoscale Res Lett 6

[140] Mu X Wu X Zhang T Go D B and Luo T 2014 Thermal transport in

graphene oxide - From ballistic extreme to amorphous limit Sci Rep 4

[141] Noh Y J Joh H I Yu J Hwang S H Lee S Lee C H Kim S Y and Youn J R

2015 Ultra-high dispersion of graphene in polymer composite via solvent free

fabrication and functionalization Sci Rep 5

[142] Yuan B Sun Y Chen X Shi Y Dai H and He S 2018 Poorly-well-dispersed

graphene Abnormal influence on flammability and fire behavior of

intumescent flame retardant Compos Part A Appl Sci Manuf 109 345ndash54

[143] Kazi S N Badarudin A Zubir M N M Ming H N Misran M Sadeghinezhad

E Mehrali M and Syuhada N I 2015 Investigation on the use of graphene oxide

as novel surfactant to stabilize weakly charged graphene nanoplatelets

Nanoscale Res Lett 10

[144] Hirata M Gotou T Horiuchi S Fujiwara M and Ohba M 2004 Thin-film

particles of graphite oxide 1 High-yield synthesis and flexibility of the

particles Carbon N Y 42 2929ndash37





[146] Yang H Zhang T Jiang M Duan Y and Zhang J 2015 Ambient pressure dried

graphene aerogels with superelasticity and multifunctionality J Mater Chem

A 3 19268ndash72

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[147] Shenoy S L Painter P C and Coleman M M 1999 The swelling and collapse

of hydrogen bonded polymer gels Polymer (Guildf) 40 4853ndash63

[148] De Silva K K H Huang H H Joshi R K and Yoshimura M 2017 Chemical

reduction of graphene oxide using green reductants Carbon N Y 119 190ndash9




Nanoscale Res Lett 10 212

[150] Lu J Do I Fukushima H Lee I and Drzal L T 2010 Stable aqueous

suspension and self-assembly of graphite nanoplatelets coated with various

polyelectrolytes J Nanomater 2010

[151] Wolf E L 2014 Practical Productions of Graphene Supply and Cost pp 19ndash38

[152] Karamikamkar S Abidli A Behzadfar E Rezaei S Naguib H E and Park C B

2019 The effect of graphene-nanoplatelets on gelation and structural integrity

of a polyvinyltrimethoxysilane-based aerogel RSC Adv 9 11503ndash20

[153] Qiu L Liu J Z Chang S L Y Wu Y and Li D 2012 Biomimetic superelastic

graphene-based cellular monoliths Nat Commun 3 1ndash7

[154] Kotal M Kim J Oh J and Oh I K 2016 Recent progress in multifunctional

graphene aerogels Front Mater 3 1ndash22



[156] Valleacutes C Beckert F Burk L Muumllhaupt R Young R J and Kinloch I A 2016

Effect of the CO ratio in graphene oxide materials on the reinforcement of

epoxy-based nanocomposites J Polym Sci Part B Polym Phys 54 281ndash91

[157] Mi H Y Jing X Huang H X Peng X F and Turng L S 2018

Superhydrophobic GrapheneCelluloseSilica Aerogel with Hierarchical

Structure as Superabsorbers for High Efficiency Selective Oil Absorption and

Recovery Ind Eng Chem Res 57 1745ndash55

[158] Patil S P Shendye P and Markert B 2020 Molecular Investigation of

174

Mechanical Properties and Fracture Behavior of Graphene Aerogel J Phys

Chem B 124 6132ndash9

[159] Qin Z Jung G S Kang M J and Buehler M J 2017 The mechanics and design

of a lightweight three-dimensional graphene assembly Sci Adv 3

[160] Barg S Perez F M Ni N Do Vale Pereira P Maher R C Garcia-Tuntildeon E

Eslava S Agnoli S Mattevi C and Saiz E 2014 Mesoscale assembly of

chemically modified graphene into complex cellular networks Nat Commun 5




[162] Worsley M A Kucheyev S O Satcher J H Hamza A V and Baumann T F

2009 Mechanically robust and electrically conductive carbon nanotube foams

Appl Phys Lett 94

[163] Chen Z Ren W Gao L Liu B Pei S and Cheng H M 2011 Three-dimensional

flexible and conductive interconnected graphene networks grown by chemical

vapour deposition Nat Mater 10 424ndash8

[164] Garciacutea-T On E Barg S Franco J Bell R Eslava S DrsquoElia E Maher R C

Guitian F and Saiz E 2015 Printing in three dimensions with Graphene Adv


[165] Zhang Q Zhang F Medarametla S P Li H Zhou C and Lin D 2016 3D

Printing of Graphene Aerogels Small 12 1702ndash8

[166] Yang J Li X Han S Zhang Y Min P Koratkar N and Yu Z Z 2016 Air-dried

high-density graphene hybrid aerogels for phase change composites with

exceptional thermal conductivity and shape stability J Mater Chem A 4

18067ndash74

[167] Gao W Zhao N Yao W Xu Z Bai H and Gao C 2017 Effect of flake size on

the mechanical properties of graphene aerogels prepared by freeze casting RSC

Adv 7 33600ndash5

[168] Liu X Pang K Yang H and Guo X 2020 Intrinsically microstructured

175

graphene aerogel exhibiting excellent mechanical performance and super-high

adsorption capacity Carbon N Y 161 146ndash52

[169] Cheng Y Zhou S Hu P Zhao G Li Y Zhang X and Han W 2017 Enhanced

mechanical thermal and electric properties of graphene aerogels via

supercritical ethanol drying and high-Temperature thermal reduction Sci Rep

7

[170] Grosse K L Bae M H Lian F Pop E and King W P 2011 Nanoscale Joule

heating Peltier cooling and current crowding at graphene-metal contacts Nat


[171] Smovzh D V Smovzh D V Kostogrud I A Boyko E V Boyko E V

Matochkin P E and Pilnik A A 2020 Joule heater based on single-layer

graphene Nanotechnology 31 335704

[172] Gupta R Rao K D M Kiruthika S and Kulkarni G U 2016 Visibly

Transparent Heaters ACS Appl Mater Interfaces 8 12559ndash75

[173] Kiruthika S Rao K D M Kumar A Gupta R and Kulkarni G U 2014 Metal

wire network based transparent conducting electrodes fabricated using

interconnected crackled layer as template Mater Res Express 1

[174] Janas D and Koziol K K 2014 A review of production methods of carbon

nanotube and graphene thin films for electrothermal applications Nanoscale 6

3037ndash45

[175] Wang H Lin S Zu D Song J Liu Z Li L Jia C Bai X Liu J Li Z Wang D

Huang Y Fang M Lei M Li B and Wu H 2019 Direct Blow Spinning of

Flexible and Transparent Ag Nanofiber Heater Adv Mater Technol 4 1900045

[176] Ragab T and Basaran C 2009 Joule heating in single-walled carbon nanotubes

J Appl Phys 106

[177] Karim N Zhang M Afroj S Koncherry V Potluri P and Novoselov K S 2018

Graphene-based surface heater for de-icing applications RSC Adv 8 16815ndash23

[178] Menzel R Barg S Miranda M Anthony D B Bawaked S M Mokhtar M Al-

Thabaiti S A Basahel S N Saiz E and Shaffer M S P 2015 Joule heating

176

characteristics of emulsion-templated graphene aerogels Adv Funct Mater 25

28ndash35




[180] Zhang T Y Zhao H M Wang D Y Wang Q Pang Y Deng N Q Cao H W

Yang Y and Ren T L 2017 A super flexible and custom-shaped graphene heater

Nanoscale 9 14357ndash63

[181] Liang C Qiu H Han Y Gu H Song P Wang L Kong J Cao D and Gu J

2019 Superior electromagnetic interference shielding 3D graphene

nanoplateletsreduced graphene oxide foamepoxy nanocomposites with high

thermal conductivity J Mater Chem C 7 2725ndash33

[182] Ghosh S Polaki S R Ajikumar P K Krishna N G and Kamruddin M 2018

Aging effects on vertical graphene nanosheets and their thermal stability Indian

J Phys 92 337ndash42

[183] Claramunt S Varea A Loacutepez-Diacuteaz D Velaacutezquez M M Cornet A and Cirera

A 2015 The importance of interbands on the interpretation of the raman

spectrum of graphene oxide J Phys Chem C 119 10123ndash9

[184] Vaškovaacute H and Křesaacutelek V 2011 Quasi real-time monitoring of epoxy resin

crosslinking via Raman microscopy Int J Math Model Methods Appl Sci 5

1197ndash204

[185] Xia T Zeng D Li Z Young R J Valleacutes C and Kinloch I A 2018 Electrically

conductive GNPepoxy composites for out-of-autoclave thermoset curing

through Joule heating Compos Sci Technol 164 304ndash12

[186] Imran K A and Shivakumar K N 2018 Enhancement of electrical conductivity

of epoxy using graphene and determination of their thermo-mechanical

properties J Reinf Plast Compos

[187] Wan Y J Yang W H Yu S H Sun R Wong C P and Liao W H 2016 Covalent

polymer functionalization of graphene for improved dielectric properties and

177

thermal stability of epoxy composites Compos Sci Technol

[188] Ghaleb Z A Mariatti M and Ariff Z M 2014 Properties of graphene

nanopowder and multi-walled carbon nanotube-filled epoxy thin-film

nanocomposites for electronic applications The effect of sonication time and

filler loading Compos Part A Appl Sci Manuf

[189] Kim J Im H Kim J M and Kim J 2012 Thermal and electrical conductivity of

Al(OH) 3 covered graphene oxide nanosheetepoxy composites J Mater Sci

[190] Li J Ma P C Chow W S To C K Tang B Z and Kim J K 2007 Correlations

between percolation threshold dispersion state and aspect ratio of carbon

nanotubes Adv Funct Mater

[191] Moosa A A Kubba F Raad M and SA A R 2016 Mechanical and Thermal

Properties of Graphene Nanoplates and Functionalized Carbon-Nanotubes

Hybrid Epoxy Nanocomposites Am J Mater Sci 6 125ndash34

[192] Zeng C Lu S Xiao X Gao J Pan L He Z and Yu J 2015 Enhanced thermal

and mechanical properties of epoxy composites by mixing noncovalently

functionalized graphene sheets Polym Bull

[193] Qiang Y Patel A and Manas-Zloczower I 2020 Enhancing microfibrillated

cellulose reinforcing efficiency in epoxy composites by graphene oxide

crosslinking Cellulose

[194] Saacutenchez-Romate X F Sans A Jimeacutenez-Suaacuterez A Campo M Urentildea A and

Prolongo S G 2020 Highly multifunctional gnpepoxy nanocomposites From

strain-sensing to joule heating applications Nanomaterials

[195] Gong X Zhang H Sun Z Zhang X Xu J Chu F Sun L and Ramakrishna S

2020 A viable method to enhance the electrical conductivity of CNT bundles

Direct in situ TEM evaluation Nanoscale 12 13095ndash102

[196] Xia D Huang P Li H and Rubio Carrero N 2020 Fast and efficient electricalndash

thermal responses of functional nanoparticle decorated nanocarbon aerogels

Chem Commun 56 14393ndash6

[197] Standard a 1996 Standard Test Methods for Plane-Strain Fracture Toughness

178

and Strain Energy Release Rate of Plastic Materials Annu B ASTM Stand 99

1ndash9

[198] Chandrasekaran S Sato N Toumllle F Muumllhaupt R Fiedler B and Schulte K

2014 Fracture toughness and failure mechanism of graphene based epoxy

composites Compos Sci Technol 97 90ndash9

[199] Sun L Gibson R F Gordaninejad F and Suhr J 2009 Energy absorption

capability of nanocomposites A review Compos Sci Technol 69 2392ndash409

[200] Ayatollahi M R Shadlou S and Shokrieh M M 2011 Fracture toughness of

epoxymulti-walled carbon nanotube nano-composites under bending and shear

loading conditions Mater Des 32 2115ndash24

[201] Tang L-C Wan Y-J Yan D Pei Y-B Zhao L Li Y-B Wu L-B Jiang J-X and

Lai G-Q 2013 The effect of graphene dispersion on the mechanical properties

of grapheneepoxy composites Carbon N Y 60 16ndash27

[202] LI J SHAM M KIM J and MAROM G 2007 Morphology and properties of

UVozone treated graphite nanoplateletepoxy nanocomposites Compos Sci

Technol 67 296ndash305

[203] Valorosi F De Meo E Blanco-Varela T Martorana B Veca A Pugno N

Kinloch I A Anagnostopoulos G Galiotis C Bertocchi F Gomez J Treossi E

Young R J and Palermo V 2020 Graphene and related materials in hierarchical

fiber composites Production techniques and key industrial benefits Compos

Sci Technol 185 107848

[204] Kinloch I A Suhr J Lou J Young R J and Ajayan P M 2018 Composites with

carbon nanotubes and graphene An outlook Science (80- ) 362 547ndash53

[205] Bortz D R Heras E G and Martin-Gullon I 2012 Impressive fatigue life and

fracture toughness improvements in graphene oxideepoxy composites

Macromolecules 45 238ndash45

[206] Watson G Starost K Bari P Faisal N Mishra S and Njuguna J 2017 Tensile

and Flexural Properties of Hybrid Graphene Oxide Epoxy Carbon Fibre

Reinforced Composites IOP Conference Series Materials Science and

179

Engineering vol 195

[207] Chen J Wu J Ge H Zhao D Liu C and Hong X 2016 Reduced graphene

oxide deposited carbon fiber reinforced polymer composites for

electromagnetic interference shielding Compos Part A Appl Sci Manuf 82

141ndash50

[208] Adak N C Chhetri S Kuila T Murmu N C Samanta P and Lee J H 2018

Effects of hydrazine reduced graphene oxide on the inter-laminar fracture

toughness of woven carbon fiberepoxy composite Compos Part B Eng 149

22ndash30

[209] Worsley M A Pauzauskie P J Olson T Y Biener J Satcher J H and Baumann

T F 2010 Synthesis of graphene aerogel with high electrical conductivity J Am


[210] Ye S Feng J and Wu P 2013 Deposition of three-dimensional graphene

aerogel on nickel foam as a binder-free supercapacitor electrode ACS Appl

Mater Interfaces 5 7122ndash9

[211] Yang M Zhao N Cui Y Gao W Zhao Q Gao C Bai H and Xie T 2017

Biomimetic Architectured Graphene Aerogel with Exceptional Strength and

Resilience ACS Nano 11 6817ndash24

[212] Scotti K L and Dunand D C 2018 Freeze casting ndash A review of processing

microstructure and properties via the open data repository FreezeCastingnet

Prog Mater Sci 94 243ndash305

[213] Zaaba N I Foo K L Hashim U Tan S J Liu W W and Voon C H 2017

Synthesis of Graphene Oxide using Modified Hummers Method Solvent

Influence Procedia Engineering vol 184 pp 469ndash77

[214] Rezania B Severin N Talyzin A V and Rabe J P 2014 Hydration of bilayered

graphene oxide Nano Lett 14 3993ndash8

[215] Imran K A and Shivakumar K N 2019 Graphene-modified carbonepoxy

nanocomposites Electrical thermal and mechanical properties J Compos

Mater 53 93ndash106

180

[216] Bhanuprakash L Parasuram S and Varghese S 2019 Experimental

investigation on graphene oxides coated carbon fibreepoxy hybrid composites

Mechanical and electrical properties Compos Sci Technol 179 134ndash44

[217] Bisht A Dasgupta K and Lahiri D 2019 Investigating the role of 3D network

of carbon nanofillers in improving the mechanical properties of carbon fiber

epoxy laminated composite Compos Part A Appl Sci Manuf 126 105601

[218] Qin W Vautard F Drzal L T and Yu J 2015 Mechanical and electrical

properties of carbon fiber composites with incorporation of graphene

nanoplatelets at the fiber-matrix interphase Compos Part B Eng 69 335ndash41

[219] Kandare E Khatibi A A Yoo S Wang R Ma J Olivier P Gleizes N and

Wang C H 2015 Improving the through-thickness thermal and electrical

conductivity of carbon fibreepoxy laminates by exploiting synergy between

graphene and silver nano-inclusions Compos Part A Appl Sci Manuf 69 72ndash

82

[220] Park Y T Qian Y Chan C Suh T Nejhad M G Macosko C W and Stein A

2015 Epoxy toughening with low graphene loading Adv Funct Mater 25 575ndash

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[221] Kinloch A J and Taylor A C 2006 The mechanical properties and fracture

behaviour of epoxy-inorganic micro- and nano-composites J Mater Sci 41

3271ndash97

[222] Zhang X Fan X Yan C Li H Zhu Y Li X and Yu L 2012 Interfacial

microstructure and properties of carbon fiber composites modified with

graphene oxide ACS Appl Mater Interfaces 4 1543ndash52

[223] Li Z Chu J Yang C Hao S Bissett M A Kinloch I A and Young R J 2018

Effect of functional groups on the agglomeration of graphene in

nanocomposites Compos Sci Technol 163 116ndash22

[224] Elmarakbi A Karagiannidis P Ciappa A Innocente F Galise F Martorana B

Bertocchi F Cristiano F Villaro Aacutebalos E and Goacutemez J 2019 3-Phase

hierarchical graphene-based epoxy nanocomposite laminates for automotive

181

applications J Mater Sci Technol 35 2169ndash77

[225] Basso M Azoti W Elmarakbi H and Elmarakbi A 2019 Multiscale simulation

of the interlaminar failure of graphene nanoplatelets reinforced fibers laminate

composite materials J Appl Polym Sci 136 1ndash11

[226] Alejandro Rodriacuteguez-Gonzaacutelez J Rubio-Gonzaacutelez C de Jesuacutes Ku-Herrera J

Ramos-Galicia L and Velasco-Santos C 2018 Effect of seawater ageing on

interlaminar fracture toughness of carbon fiberepoxy composites containing

carbon nanofillers J Reinf Plast Compos 37 1346ndash59

[227] Kumar A and Roy S 2018 Characterization of mixed mode fracture properties

of nanographene reinforced epoxy and Mode I delamination of its carbon fiber

composite Compos Part B Eng 134 98ndash105

[228] Rodriacuteguez-Gonzaacutelez J A Rubio-Gonzaacutelez C Jimeacutenez-Mora M Ramos-

Galicia L and Velasco-Santos C 2018 Influence of the Hybrid Combination of

Multiwalled Carbon Nanotubes and Graphene Oxide on Interlaminar

Mechanical Properties of Carbon FiberEpoxy Laminates Appl Compos


[229] Gogotsi Y and Anasori B 2019 The Rise of MXenes ACS Nano 13 8491ndash4

[230] Persson I Naumlslund L Aring Halim J Barsoum M W Darakchieva V Palisaitis J

Rosen J and Persson P O Aring 2018 On the organization and thermal behavior of

functional groups on Ti3C2 MXene surfaces in vacuum 2D Mater 5 015002

[231] Zhang N Hong Y Yazdanparast S and Zaeem M A 2018 Superior structural

elastic and electronic properties of 2D titanium nitride MXenes over carbide

MXenes A comprehensive first principles study 2D Mater 5 045004

[232] Garg R Agarwal A and Agarwal M 2020 A Review on MXene for energy

storage application Effect of interlayer distance Mater Res Express 7 022001

[233] Park T H Yu S Koo M Kim H Kim E H Park J E Ok B Kim B Noh S H

Park C Kim E Koo C M and Park C 2019 Shape-Adaptable 2D Titanium

Carbide (MXene) Heater ACS Nano 13 6835ndash44

[234] Yasaei P Tu Q Xu Y Verger L Wu J Barsoum M W Shekhawat G S and

182

Dravid V P 2019 Mapping Hot Spots at Heterogeneities of Few-Layer Ti 3 C 2

MXene Sheets ACS Nano 13 3301ndash9



3 022001

[236] Yang W Byun J J Yang J Moissinac F P Peng Y Tontini G Dryfe R A W

and Barg S 2020 Freeze‐assisted Tape Casting of Vertically Aligned MXene

Films for High Rate Performance Supercapacitors Energy Environ Mater 3

380ndash8

[237] Jeong Y G and An J E 2014 Effects of mixed carbon filler composition on

electric heating behavior of thermally-cured epoxy-based composite films

Compos Part A Appl Sci Manuf 56 1ndash7

[238] El-Tantawy F 2001 Joule heating treatments of conductive butyl

rubberceramic superconductor composites A new way for improving the

stability and reproducibility Eur Polym J 37 565ndash74

[239] Halim J Cook K M Naguib M Eklund P Gogotsi Y Rosen J and Barsoum

M W 2016 X-ray photoelectron spectroscopy of select multi-layered transition

metal carbides (MXenes) Appl Surf Sci 362 406ndash17

[240] Shah S A Habib T Gao H Gao P Sun W Green M J and Radovic M 2017

Template-free 3D titanium carbide (Ti3C2Tx) MXene particles crumpled by

capillary forces Chem Commun 53 400ndash3

[241] Xue Y Liu J Chen H Wang R Li D Qu J and Dai L 2012 Nitrogen-doped

graphene foams as metal-free counter electrodes in high-performance dye-

sensitized solar cells Angew Chemie - Int Ed 51 12124ndash7

[242] Aghamohammadi H Amousa N and Eslami-Farsani R 2021 Recent advances

in developing the MXenepolymer nanocomposites with multiple properties A

review study Synth Met

[243] Wang L Chen L Song P Liang C Lu Y Qiu H Zhang Y Kong J and Gu J

2019 Fabrication on the annealed Ti3C2Tx MXeneEpoxy nanocomposites for

183

electromagnetic interference shielding application Compos Part B Eng

[244] Kang T J Kim T Seo S M Park Y J and Kim Y H 2011 Thickness-dependent

thermal resistance of a transparent glass heater with a single-walled carbon

nanotube coating Carbon N Y 49 1087ndash93


Graphene FoamndashPolymer Composite with Superior Deicing Efficiency and


[246] Pan L Liu Z kızıltaş O Zhong L Pang X Wang F Zhu Y Ma W and Lv Y

2020 Carbon fiberpoly ether ether ketone composites modified with graphene

for electro-thermal deicing applications Compos Sci Technol

[247] Raji A R O Varadhachary T Nan K Wang T Lin J Ji Y Genorio B Zhu Y

Kittrell C and Tour J M 2016 Composites of graphene nanoribbon stacks and

epoxy for joule heating and deicing of surfaces ACS Appl Mater Interfaces 8

3551ndash6

[248] Zhang Q Yu Y Yang K Zhang B Zhao K Xiong G and Zhang X 2017

Mechanically robust and electrically conductive graphene-paperglass-

fibersepoxy composites for stimuli-responsive sensors and Joule heating

deicers Carbon N Y

[249] Luong D X Yang K Yoon J Singh S P Wang T Arnusch C J and Tour J M

2019 Laser-Induced Graphene Composites as Multifunctional Surfaces ACS

Nano

[250] Wang Q W Zhang H Bin Liu J Zhao S Xie X Liu L Yang R Koratkar N

and Yu Z Z 2019 Multifunctional and Water-Resistant MXene-Decorated

Polyester Textiles with Outstanding Electromagnetic Interference Shielding

and Joule Heating Performances Adv Funct Mater 29

[251] An J E and Jeong Y G 2013 Structure and electric heating performance of

grapheneepoxy composite films Eur Polym J 49 1322ndash30

[252] Zhang X F Li D Liu K Tong J and Yi X S 2019 Flexible graphene-coated

carbon fiber veilpolydimethylsiloxane mats as electrothermal materials with

184

rapid responsiveness Int J Light Mater Manuf 2 241ndash9

2

Contents

Contents 2

List of Tables 6

List of Figures 8

List of Abbreviations 18

List of Pubilications 19

Abstract 20

Declaration 21

Copyright 22

Acknowledgments 23

1 Chapter 1 Introduction 24

11 Polymer materials 24

12 2D materials 25

121 Graphene 25

122 MXene 27

123 Other 2D material 29

13 Polymer nanocomposites 29

131 Nanocomposites with 2D materials 30

132 Epoxy2D materials based nanocomposites 30

133 Aims and objectives 31

2 Chapter 2 Literature Review 36

21 Preparation of 2D materials-based aerogel 36

211 Hydrothermal reduction method 36

212 Cross-linking method 40

213 Chemical reduction method 42

214 Ice-template method 44

22 Preparation of 2D materials aerogel-based polymer nanocomposites 51

3

221 Dip coating 51











25 Conclusion 66



31 Introduction 67


321 Materials 69










34 Conclusion 86


88

4

41 Introduction 89


421 Materials 90












44 Conclusion 107


composites 109

51 Introduction 109

52 Experimental 111

521 Materials 111










5




54 Conclusion 125


Applications 127

61 Introduction 127


621 Materials 128












64 Conclusion 149


71 Conclusions 151

72 Future work 156

References 158

6

List of Tables


composites 66





91




composites 117









146








7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright







Policy You are required to submit your thesis electronically Page 11 of 25 with licensing


copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


3

221 Dip coating 51











25 Conclusion 66



31 Introduction 67


321 Materials 69










34 Conclusion 86


88

4

41 Introduction 89


421 Materials 90












44 Conclusion 107


composites 109

51 Introduction 109

52 Experimental 111

521 Materials 111










5




54 Conclusion 125


Applications 127

61 Introduction 127


621 Materials 128












64 Conclusion 149


71 Conclusions 151

72 Future work 156

References 158

6

List of Tables


composites 66





91




composites 117









146








7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright









copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


4

41 Introduction 89


421 Materials 90












44 Conclusion 107


composites 109

51 Introduction 109

52 Experimental 111

521 Materials 111










5




54 Conclusion 125


Applications 127

61 Introduction 127


621 Materials 128












64 Conclusion 149


71 Conclusions 151

72 Future work 156

References 158

6

List of Tables


composites 66





91




composites 117









146








7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright









copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


5




54 Conclusion 125


Applications 127

61 Introduction 127


621 Materials 128












64 Conclusion 149


71 Conclusions 151

72 Future work 156

References 158

6

List of Tables


composites 66





91




composites 117









146








7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright









copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


6

List of Tables


composites 66





91




composites 117









146








7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright









copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


7


and h height) 155

8

List of Figures









MXene flakes[20] 28








aerogel[60] 38











9




















45










10





























composites[110] 52

11















59



60







62





12
















(GNP) flakes 71














13



























times 84



14











aerogel[104153167168] 85



















15




















114










16






test 121






130










134








17

















18


0D Zero dimensional

1D One dimensional

2D Two dimensional




CB Carbon black

CNT Carbon nanotube

GO Graphene oxide


GA Graphene aerogel

CFs Graphene foams






PA Polyamide







19



















submitted)

20

Abstract

































21

Declaration



22

Copyright









copies made














23

Acknowledgments












24
























25


12 2D materials





2D nanomaterials[9]

121 Graphene





12)

26


















27

















122 MXene











28




















29
























30


conductivities[33]
























31
























bull



32










structure[50]


















33



uniformly dispersed








based composites















34

















improvements










35








applications


36

























37

















38










aerogel[60]










39












modelling[76]












40


















41



















42



aerogel paper[93]













of rGO





43













weight[98]







44

















45









15 times








46












47



















48





nm












49





contaminated water











50


















51










221 Dip coating












52


composites[110]






conditions[111]











53








polymer composites


aerogel)[52]

54





















55























56





57



















air unlike PDMS

58











59













60










61





GrF[120]










62






polyimide[126]












63



content[113]















system

64













immobilization[128]



65


























66


composites

Material

Property


Electrical

properties



PANI sponge




Mechanical

properties


PDMSepoxy


Thermal

properties

GrapheneMXeneBoron

nitride aerogel-

PDMSepoxy Polyamide



material

25 Conclusion





67
















31 Introduction










68























69









321 Materials







nm (Figure 32)




70















33)



71


flakes















72










pH















accuracy

73




slow recovery rate





120590(120596) = |119884lowast(120596)|119905

119860 =

1


119860 (31)






slow recovery rate



74


















75





time[148]











36)

76














77









Sample

Chemical

reduction

time

(minutes)

Thermal

reduction

temperature

(oC)

Thermal

reduction

time

(minutes)

Density

(mgcm3)

Oxygen

content

(at)

CO

ratio

Sample

volume

shrinkage

CR0 0 0 0 332 plusmn 21 401 15 97

CR0TR300 0 300 40 313 plusmn 11 85 108 65

CR5TR300 5 300 40 279 plusmn 07 59

CR10TR300 10 300 40 273 plusmn 06 53

CR15TR300 15 300 40 274 plusmn 12 57

CR20TR300 20 300 40 253 plusmn 09 52

CR25TR300 25 300 40 256 plusmn 04 64

CR30TR300 30 300 40 224 plusmn 13 56

CR35TR300 35 300 40 232 plusmn 07 66 142 59

CR40TR300 40 300 40 243 plusmn 13 43

CR45TR300 45 300 40 224 plusmn 05 63

CR50TR300 50 300 40 236 plusmn 07 59

CR55TR300 55 300 40 221 plusmn 09 55

CR60TR300 60 300 40 223 plusmn 06 57 158 57

CR60TR800 60 800 40 208 plusmn 08 32 303 72

78

















79


















(Figure 38)


80


















81






82















83

















the Raman results

84
























85
























86














34 Conclusion




87













88















89

41 Introduction




























90






421 Materials


















91








10 respectively





in mg)

rGOGNP

aerogel

density

(mgcm3)

Sample Graphene

loading

(wt)

GA-2 5 (GO) + 10 (GNP) ~132 EGAC-2 125

GA-4 5 (GO) + 20 (GNP) ~233 EGAC-4 21

GA-6 5 (GO) + 30 (GNP) ~334 EGAC-6 3

GA-8 5 (GO) + 40 (GNP) ~426 EGAC-8 375

GA-10 5 (GO) + 50 (GNP) ~534 EGAC-10 46

92










93














326








equation

120582 = 119862119901 times 120588 times 120572 (41)

94













1198701119862 =119875119898119886119909119891(119886

119882frasl )

11986111988212 119891(119909) = 6radic119886119908frasl



1198822frasl )]

(1+2119886119882frasl )(1minus119886

119882frasl )32 (42)











95



















96





















97




















98


basedEP composites


(wt)


conductivity (Sm)

Ref

EGAC-2

EGAC-10

125

46


492

This thesis






EPRGO

aerogels
















99




with EGC and epoxy
















100




















101
























119876 = 1198942 times 119877 times 119905 (43)






102









103







of 5V




relation[195]

120590 prop ln (119879119869119867) (44)








approaches








104













from the Ref [196]



105




















106






















(Figure 49 d)

107



44 Conclusion












108

nanoheater

















109














51 Introduction













110






























111




52 Experimental

521 Materials











Chapter 3 [213]












112
























113










326

114













115



in Figure 52 c

















116
















can be observed

117


composites


CFEP

GOA-

CFEP

rGOA-CFEP

Density

(gcm3)






118









119






























120



basedCF composites


10 vol rGO

reinforced CFepoxy

composites



mechanism and then



thesis

10 wt

GNP reinforced

CFepoxy composites


GO coated CFepoxy

composites





moulding


08 wt hybrid


GNP 50 CNT 25

nanodiamond)


10-5 to 395 times 10-5 Sm)

[217]

GNP reinforced

CFepoxy composites



solution












121









investigation







122





control CFEP





















123










path

124










reasons


matrix











basedCF composites


enhancement

Ref

10 vol GO

reinforced CFepoxy



K1c + 288

G1c + 676

This thesis

125

composites

06 wt GNP

reinforced CFepoxy

composites


2 vol GNP

reinforced CFepoxy

composites


10 wt GNP

reinforced CFepoxy

composites


2032 Jm2)

[215]

08 wt hybrid


GNP 50 CNT

25 nanodiamond)


02 wt hydrazine

reduced GO

reinforced CFepoxy

composites


025 wt RGO

reinforced CFepoxy

composites


05 wt GNP CF

reinforced epoxy

composites


025 wt GO

reinforced CFepoxy

composites




54 Conclusion






126







127















61 Introduction











128












621 Materials














129
















oven

130













131








equation [237][238]

(119879119905 minus 1198790

119879119898 minus 1198790) = 1 - exp (-

119905

120591119892) (61)





132

hr+c = 1198681198881198810

119879119898 minus 1198790 (62)


with Equation 63

(119879119905 minus 1198790

119879119898 minus 1198790) = exp (-

119905

120591119889) (63)




















133



















134



















135















136




137


















138






139












Joule Heating test

Region BE (eV) FWHM

(eV)


Ti 2p32 (2p12) 4555 (4617) 15 (15) 81 Ti

4559 (4612) 18 (18) 199 Ti2+

4567 (4624) 20 (20) 355 Ti3+

4582 (4637) 20 (20) 208 TiO2

4594 (4652) 12 (12) 83 TiO2-xFx

4601 (4661) 12 (12) 74 C-Ti-Fx

C 1s 2820 10 76 C-Ti-Tx

2840 13 91 Car

285 13 354 Cal

2856 12 190 C-Oar

2862 10 112 C-Oal

287 13 165 Epoxy

2830 06 12 Carbide

O 1s 5302 19 327 TiO2

140





5352 03 10 Al(OF)x

5341 20 147 Epoxy1

5337 13 129 Epoxy2

5327 15 221 Epoxy3

F 1s 6854 13 498 C-Ti-Fx

6852 17 364 TiO2-xFx

6867 13 138 AlFx

0 Al(OF)x
















141




thread heater [233]












142
















143



voltage of 2V













144



























145















146










epoxy

resinTi3C2Tx

aerogel

composite


125 645plusmn10 0035 868plusmn65

15 669plusmn18 0031 724plusmn11

175 723plusmn08 0027 670plusmn32







Equation 61 and 63

147





148





















149















Sample Ti

(at )

C

(at )

TiC O

(at )

F

(at )

Cl

(at )

Ti3C2Tx aerogel

(before) 4780 3700 129 880 280 360

Ti3C2Tx aerogel

(after) 5090 3310 153 860 290 440

Epoxy

resinTi3C2Tx

aerogel composite

(before)

2560 5560 046 1470 217 197

Epoxy

resinTi3C2Tx

aerogel composite

(after)

2430 5400 045 1640 360 174

64 Conclusion


150














151


71 Conclusions







as below




















152



























Joule heating test



153












here




based epoxy

composites

MXene aerogel based

epoxy composites




Current (A) 065 51



temperature (degC)

134 166






154












Materials


Voltage applied

(Volts)

Steady-state

temperature (degC)

Response

time (sec)

Heating rate

(deg Cmin)

Power density

(Wcm2 and Wcm3)

Epoxygraphene-based


10

(13times13times03)

3 134 140 574 0825

5 213 140 913 31102


(1times04times012 )[245] 25 ~40 ~60 ~40 25208

CfPEEK composites

(1times1times03) [246] ~20 ~7 100 42 ~40~120

EpoxyGNR

composite

(25 times 06 times 05) [247]

40 ~170 ~500 ~20 53

BNrCNT aerogel [196] 55 90 - 580 ~

BNrGO aerogel [196] 35 125 - 580 ~

Grphene-glass fiber

composites


~ ~210 ~600 ~21 10733 ˣ 107

Laser-induced

graphenePDMS


6 ~100 840 71 ~




155



















and h height)

Materials


Voltage

applied

(Volts)

Steady-state

temper-ature

(degC)

Respo-nse

time (sec)

Heatin-g rate

(deg Cmin)

Power density

(Wcm2 and

Wcm3)

Energy

density

(Wcm3h)

Cycles

Ti3C2TX aerogel

(13times13times03)

2 483 35 828 79263 026 100


(13times13times03) 2 123 140 527 61203 079 100

3 166 160 623 139463 206 -

MMTTi3C2TX film

(2times05) [59] 3 60 120 30 06 - 10

PPyTi3C2TX textile

(4times1) [250] 3 57 ~90 ~38 007 - 50

156

Laser-induced rGO

(2times2times0005) [179] 9 135 10 810 0389778 022 -

Au wire networks

(013times013) [173]

3 ~ 40 ~ 300 ~8 75 - -

rGOEpoxy film

(05times2) [251]

30 126 ~ 20 ~378 18 - 10

EpoxyGnP film

(05times2) [237]

20 40 ~ 20 ~120 008 - 10

EpoxyGNPMWCNT

film

(05times2) [237]

120 ~ 20 ~360 8 - 10

EpoxyGNR composite

(25 times 06 times 05) [247] 40 ~170 ~500 ~20 53106 147 -


rovings

(10 times 10) [177]

10 1008 180 ~253 - - -

GNP-coated carbon

fiber veilPDMS mats

(20 times 20) [252]

65 2974 50 125 111 - -









72 Future work




157














humidity







well-appreciated








158

References







engineering





















159




















Mater 21 4683ndash6










160



























3 022001



161






3507ndash14






6 112486ndash92










2889ndash93





166ndash77



162


Nanotechnology 22






Y 46 806ndash17






















163





28 6731ndash41












13103ndash7













164















21 2180ndash4





C 113 13651ndash7







5



165






























166


Bull 63 248ndash52













19532ndash5










2934ndash41





167















A 3 19144ndash7















168

















Rep 3






Networks Sci Rep 5







169







Dielectr























170









Small 14









50074ndash80












171






























172





























A 3 19268ndash72

173






























174













Appl Phys Lett 94












18067ndash74



Adv 7 33600ndash5


175






7














3037ndash45





J Appl Phys 106





176


28ndash35



















1197ndash204









177






























178


1ndash9




























179

Engineering vol 195




141ndash50




22ndash30




















Mater 53 93ndash106

180














82



85



3271ndash97










181






























182





3 022001




380ndash8





















183














3551ndash6




deicers Carbon N Y



Nano









184


epoxy/2d materials aerogel composites with multifunctional

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