research article mechanical and electrical properties of

Research ArticleMechanical and Electrical Properties ofStyrene-Isoprene-Styrene Copolymer Doped withExpanded Graphite Nanoplatelets

Zdenko Špitalskyacute1 Jaacuten Kratochviacutela1 Katariacutena Csomorovaacute1 Igor Krupa2

Manuel P F Graccedila3 and Luis C Costa3

1Polymer Institute Slovak Academy of Sciences Dubravska Cesta 9 845 41 Bratislava Slovakia2Center for Advanced Materials Qatar University PO Box 2713 Doha Qatar3I3N and Physics Department University of Aveiro 3810-193 Aveiro Portugal

Correspondence should be addressed to Zdenko Spitalsky upolspizsavbask

Received 6 March 2015 Accepted 9 July 2015

Academic Editor Nay Ming Huang

Copyright copy 2015 Zdenko Spitalsky et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The molecular dynamics of a triblock copolymer and of expanded graphite nanoplatelets were investigated Composites wereprepared using the solution techniqueThe effects of filler addition and of filler-matrix interactionswere investigated using dielectricrelaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA) Only one relaxation was observed by DRS which wasassociated with the relaxation of the main polymer chain Both DRS and DMA demonstrated that the addition of the filler doesnot cause a significant change in either the temperature of the relaxation or its activation energy which suggests the presence ofweak interactions between the filler and matrix The storage modulus of the composites increased with increasing filler contentThe composite containing 8 filler exhibited a storage modulus increase of approximately 394 in the rubber area Using the DCelectrical conductivity measurements the electrical percolation threshold was determined to be approximately 5 The dielectricpermittivity and conductivity in the microwave region were determined confirming that percolating behavior and the criticalthreshold concentration

1 Introduction

Graphene is a flat monolayer of carbon atoms that are tightlypacked into a two-dimensional (2D) carbon honeycomb lat-tice Recently graphene has attracted considerable attentiondue to its high surface area low density and electrical andmechanical properties [1ndash7] The incorporation of grapheneparticles into polymermatrices promises to produce compos-ites that possess unusual properties [8ndash16]

The electrical conductivity of an insulating polymer canbe enhanced by adding different conducting particles such ascarbon [1ndash15] metals or even another conducting polymer[16] A low electrical percolation threshold can also beachieved with graphene sheets An electrical percolationthreshold of 005wt was observed in the polyethylene-terephthalate matrix [17] Additionally an improvement

in mechanical properties was observed in thermoplasticpolyurethane and the incorporation of 3 wt of ultra-thin graphene sheets improves the storage modulus (by300) shear viscosity (by 150) and thermal stability ofthe material Further improvement was observed when theoxidized formof graphenewas applied this improvementwaslikely due to improved chemical interactions [18] Moreovergraphene-based composites have been reported to possessa novel behavior photoactuation [19] Compared to othercarbon-based fillers the graphene-based nanopellets exhib-ited the best actuation behavior [20] This result highlightsthe potential of these elastomer-based graphene composites

The physical properties of a composite are always deter-mined by the employed processing technique Comparedto the solution mixing method the in situ preparationof graphene oxidepolyurethane composites resulted in an

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2015 Article ID 168485 9 pageshttpdxdoiorg1011552015168485

2 Journal of Nanomaterials

improvement in themodulusThe observed reinforcing effectwas attributed to the improved interactions obtained duringthis in situ method [21] Similar results were also obtained inthe thermoplastic polyurethane matrix [22] however only aweak reinforcement effect has been reported in polyethylenematric [23]Thephysical properties of the grapheme-polymercomposites depend also highly on the degree of cross-linkingand the finalmorphology [24]This result can be attributed tothe decreased aspect ratio of the filler as it can emerge eitherin a wrinkled conformation of the filler [25] or due to particleattrition during mixing [26] It was also reported that thesonication of expanded graphite in a viscous solution enablesthe further separation of graphene platelets into smallernanometer-sized platelets [27] As the expanded graphenelayers are intercalated by polymer chains it is hypothesizedthat the sonicated expanded graphene possesses a largernumber of smaller platelets and therefore serves as a moreefficient nanofiller [28]

The need to protect electronic components againstelectromagnetic interference is very important particularlyat microwave frequencies where wireless communicationsoccur The effects of electromagnetic interference can bedecreased by positioning a shielding material between thesource of the electromagnetic field and the electronic compo-nent Graphene composites are a good possibility for achiev-ing that objectiveThenmicrowave dielectric properties weremeasured using the resonant cavity method [29 30] To thebest of our knowledge there is only one work concerningmicrowave spectroscopy study of graphene-based elastomercomposite materials when the microwave permittivity ofstyrene-butadiene rubber composite was unaffected by strainup to 8 [31]

Therefore in this study expanded graphite obtainedusing the solution sonication techniquewas employed In thispaper the results from a study on the molecular dynamics ofa styrene-isoprene-styrene and graphene sheet composite arepresented The composites were prepared using the solutiontechnique and their percolation behaviors impedance spec-tra and mechanical properties were characterized

2 Materials and Methods

21 Materials GFG50 expanded graphite particles withan average size of 50 120583m were obtained from SGL Tech-nologies GmbH Germany Kraton D1165 PT (a linear tri-block copolymer based on styrene and isoprene with apolystyrene content of 30) was purchased from KratonPerformance Polymers Inc Toluene with a pa purity waspurchased from Sigma-Aldrich and was used without furtherpurification

A dispersion of GFG50 in 50mL of toluene was producedby sonication in an ultrasonic bath for 20 minutes followedby mixing with a polymer solution (2 g of polymer wasdissolved in 20mL of toluene under rigorous stirring) Thethin films were casted onto a Teflon array The thin filmswith a nanofiller concentration of up to 10wt exhibited anaverage thickness of approximately 400 120583m

22 Polymer Characterization XRD analysis was conductedusing a Bruker D8 DISCOVER diffractometer equipped withanX-ray tubewith a rotatingCu anode operating at 12 kWAllof the measurements were performed using a parallel beamgeometry with a parabolic Goebel mirror positioned in theprimary beam

The X-ray diffraction patterns were recorded using agrazing incidence setup with an angle of incidence 2∘ Thesurface morphologies were examined using scanning elec-tron microscopy with a dual beam (FIBSEM) MicroscopeQuanta 3D 200i (FEI)The free surface and the cross sectionsof thesematerials were investigatedAll of the specimensweresputter coated with a thin layer of gold prior to examination

TGA measurements were performed using a MettlerToledo TGASDTA 851 instrument in a nitrogen flow(30mLmin) using a heating rate of 10∘Cmin over the tem-perature range from 25∘C to 800∘C Indium and aluminumwere used for temperature calibrationThe amount of sampleused was 2mg Two parallel runs were performed for eachsample

Viscoelastic measurements were performed using a TAInstruments DMAQ800 dynamicmechanical analyzer Sam-ples with uniform shapes were measured in the moduletensile multifrequency strain at 10Hz and a strain amplitudeof 5 120583m The loss tangent (tan 120575) and storage modulus wereobtained from minus100∘C to 130∘C using a heating rate of2∘Cmin

For the electrical measurements of the samples contactswere made by painting both sides of the polymer samplewith silver paste simulating a parallel plate capacitor witha surface area of 1 cm2 and a distance between electrodes ofapproximately 04mm

DC conductivity measurements were conducted usingthe standard two contacts with the guard method using aKeithley 617 Electrometer at temperatures between minus110∘Cand 90∘C in an inert atmosphere

Dielectric measurements were performed using an Agi-lent 4294A Precision Impedance Analyzer for frequenciesbetween 40Hz and 2MHz The general approach is to applyan electrical stimulus and to observe the response of themate-rial It is then assumed that the properties of the electrode-material system are time invariant which is an importantassumption for the measurement method The amplitudeof the applied voltage was 1 V From a practical point ofview dielectric spectroscopy can provide a measurementof the complex permittivity 120576lowast(120596) = 1205761015840(120596) minus 11989412057610158401015840(120596) orderived quantities related to it such as the dielectricmodulus119872 = 120576

minus1 The macroscopic properties such as impedance119885lowast

(120596) = 1198851015840

(120596) minus 11989411988510158401015840

(120596) or admittance 119884 = 119885minus1 canalso be obtained The interrelations between these quantitiesare simple when their geometric parameters (shape size andthickness) are known In our case the measured values wereused to calculate the dielectric complex modulus (119872lowast) usinga parallel RC (Resistance-Capacitor) model of the sampleThe estimated relative errors on both the real and imaginaryparts of the complex permittivity were less than 2

For the microwave dielectric measurements the resonantcavity method at 27 GHz was used The samples used were

Journal of Nanomaterials 3

Inte

nsity

10 20 30 40 50 60

2120579 (∘)

10

5

050

Figure 1 WAXS patterns of different samples neat polymer matrix(0) and three different composites with 05 5 and 10wt of fillerrespectively

prepared as cylinders with a height of 8mm and a diameterof 4mm In this method the shift in the resonant frequencyof the cavity Δ119891 caused by the insertion of a sample ina cavity sample which is related to the real part of thecomplex permittivity 1205761015840 and the change in the inverse of thequality factor of the cavity Δ(1119876) which is associated withthe imaginary part 12057610158401015840 were measured The mathematicalformalism is simple when we consider only the first-orderperturbation in the electric field caused by the sample [32]

1205761015840

= 119870Δ119891

1198910

119881

V+ 1

12057610158401015840

=119870

2Δ(

1119876)119881

V

(1)

where 119870 is a constant related to the depolarization factorwhich depends upon the geometric parameters 119891

0is the

resonance frequency of the cavity V is the volume of thesample and 119881 is the volume of the cavity By using a samplewith a known permittivity as a reference it is possible tocalculate the constant 119870 In this case a PTFE sample withthe same shape and dimensions of the samples was used asa reference These measurements were performed using anAgilent 8753DNetwork Analyzer coupled to a 27GHz cavityresonator

3 Results and Discussion

Figure 1 shows the WAXS patterns of different samples Inthis figure 4 lines can be observed for the neat polymer andfor 3 composites with different concentrations of nanofiller(05 5 and 10wt) The WAXS pattern of the neat polymermatrix contains only one broad peak at approximately 2Θ =185∘ The addition of expanded graphite introduced a newpeak at 2Θ = 265∘ corresponding to the 002 reflection peakof pure graphite The intensity of this peak increased as

the concentration of GFG50 in the sample increased Noother peaks at lower 2Θ angles were observed which indi-cates no exfoliation to longer distances between individuallayers of graphite This scattering profile corresponds to thatof the neat matrix polymer with separate phase (microcom-posite) [10] However we believe that the sonication stepallowed for further separation of graphite platelets to indi-vidual graphene sheets as observed in the scanning electronmicrographs of the composites Because the concentration ofgraphene sheets is significantly lower than the concentrationof expanded graphite particles which have the dominantpeak in the WAXS pattern no related signal was observedIn addition peaks of the graphene sheets can also be coveredby the broad peak of the amorphous polymer at 2Θ = 185∘

As shown in Figure 2 the nanocomposite surface is notcompletely flat This slight waviness was created during theevaporation of the solvent Small graphene particles (whitelines sizes up to 10 120583m in length but only few nanometersin thickness) are observed at the surface and are orientedout from the surface The entire surface is homogeneousfor all of the samples with the same texture As indicatedby the cross-sectional area this composite is homogeneousthrough the entire thickness without preferred sedimentationat one side however drying the free-standing solvent-castedfilms required a few hours Therefore the distribution ofgraphene particles is isotropic meaning that the nanofillerwas homogeneously separated in the solvents and that theaddition of polymer solution caused the filler to be coveredwith polymer chains which prevented their restacking Thestarting carbon filler dimension was approximately 50120583mand its thickness after sonication is at the nanometer scalewhich is evidence that the sonication process exfoliated largegraphite particles to thinner ones [33]

Thermogravimetric analysis (TGA)was performed underan inert atmosphere to avoid oxidation processes Asobserved from the TGA curves (Figure 3) the neat polymeris stable up to 310∘C when rapid thermal degradation beganAt 11987950

= 391∘C 50wt of the polymer is decomposed Theentire neat polymer is decomposed at 471∘C The addition ofexpanded graphite has only a weak effect on thermal stabilityhowever expanded graphite could act as fire retardant [34]The onset of thermal degradation is the same as that for theneat polymer T

50value is only slightly shifted by approxi-

mately 11∘C to higher temperatures up to 402∘C (the valueincreased as the content of nanofiller increased)The thermaldegradation of the composites was completed at the sametemperature as for the neat polymermatrix Only the amountof residue increased as the content of GFG50 particlesincreased (graphite cannot be removed by combustion undera nitrogen atmosphere at this low temperature)

Figure 4 shows the storage modulus and tan 120575 of the neatpolymer matrix curveThe values of the measured propertiesat selected temperatures are presented in Table 1

As shown there are no significant changes in the valueof the glass transition temperature between the neat materialand composites The first transition is close to minus40∘C Thistransition is caused by the isoprene part of the SIS blockcopolymer The second transition caused by the styrene partof the copolymer occurs at an average temperature of 110∘C


(a) (b)

(c)

Figure 2 SEM images of GFG50 in Kraton (a) cross-sectional area of the whole composite for 5wt GFG50 (b) detailed view of cross-sectional area (c) surface area of nanocomposite

110

100

90

80

70

60

50

40

30

20

10

0

0 100 200 300 400 500 600 700 800

T (∘C)

Wei

ght l

oss (

)

005124

56810

Figure 3 TGA curves for all samples


Table 1 Summary of the thermal and mechanical properties obtained from DMAmeasurements

119909 1198791198921

by tan 120575 (∘C) SD 1198791198922

by tan 120575 (∘C) SD 1198641015840minus100∘C (MPa) SD 119864

1015840

25∘C (MPa) SD 119864101584050∘C (MPa) SD 119864101584080∘C (MPa) SD0 minus398 02 1107 18 27965 4009 54 02 45 03 36 0105 minus397 04 1110 17 12289 4774 42 16 31 14 23 1210 minus404 10 1108 17 32565 5805 67 25 55 27 42 2420 minus393 14 1116 04 34715 2977 84 17 55 30 48 2140 minus383 31 1099 09 36120 5968 123 14 102 03 78 0450 minus394 09 1113 08 35610 2871 123 15 104 11 88 0260 minus395 08 1105 13 38895 8054 149 03 119 13 93 1080 minus388 01 1106 15 47285 2383 267 09 219 24 154 46100 minus402 11 1073 16 35050 15132 265 37 253 34 184 49SD standard deviation119879119892 glass transition temperature119864

1015840 storage modulus at selected temperature

2500

2000

1500

1000

500

0

Stor

age m

odul

us (M

Pa)

minus100 minus50 0 50 100 150

Temperature (∘C)

15

10

05

00ta

n 120575

Figure 4 Temperature dependence of storage modulus and tan 120575 for neat polymer matrix

[30] This behavior suggests very poor interactions betweenthe filler and polymer chains however an increase of 6∘C inthe PS glass transition temperature was previously observedfor functionalized graphene sheets in SIS copolymer [35]

The storage modulus values exhibit an increasing trend atall testing temperatures as the content of GFG50 increasesThe most significant reinforcement effect was observed forthe sample with 8wt nanofiller in which the storagemodulus 1198641015840 was increased by 69 to 47GPa in the glassarea and by 394 to 267MPa in the rubber area (at 25∘C)The mechanical properties of SIS copolymer with grapheneparticles were also studied by Ansari et al in tensile mode[36] when the reinforcement was observed with increasingconcentration of filler up to 1 wt and then the decrease ofmodulus proceeded for higher concentrations

Figure 5 presents the DC electrical conductivity as afunction of the filler concentration at 27∘C (300K) At lowconcentrations the small increase in the conductivity ofthe composite can be attributed to the mobility of a smallnumber of charged particles through the system without acontinuous conductive path At the percolation thresholdconcentration (5wt) the conductivity sharply increasesdue to the formation of a continuous conductive path

001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

1E minus 12

0 2 4 6 8 10

Concentration (wt)

120590D

C(S

mminus1)

Figure 5 DC electrical conductivity 120590DC as a function of the fillerconcentration at 27∘C (300K)

developed in the polymer matrix and finally at higherconcentrations the further addition of filler has a marginaleffect on the conductivity The value of percolation thresholdis significantly higher than for other polymer composites


0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE

Figure 6 Transmission of the 27 GHz resonant cavity with theempty cavity and with different samples that is PTFE and copoly-mer matrix with 1 wt 4wt and 5wt conducting fillers

001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)

Figure 7 Conductivity at microwave frequencies (120590MW) at 27∘C(300K) (◻)TheDC conductivity (∘) is also included for comparison(120590DC)

with graphite nanoplatelets [17 37] but is affected by lowinteraction between the filler and the polymer matrix causedby microstructure of expanded graphite particles as wasobserved on WAXS [16]

The percolation behavior can also be observed in theAC conductivity and permittivity measurements Figure 6shows the transmission of the 27 GHz resonant cavity withthe empty cavity and with different samples that is PTFEand copolymermatrix with concentration 1 wt 4wt and5wt conducting fillers It can be observed that the highestperturbation is observed for concentration 5wt where thepercolation path is formedThis perturbation corresponds tohighest real and imaginary parts of the complex permittivity

Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)

it is possible to calculate the conductivity at microwavefrequencies which is shown in Figure 7 (open squares) atT =27∘C (300K) in which the DC conductivity is included forcomparison (open circles)

60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)

Figure 8 Dielectric constants measured at several frequencies (∘ atGHz ◻ at kHz and 998779 at MHz) at a constant temperature of 27∘C(300K)

16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K

Figure 9 Real part of the complex permittivity for a sample withconcentration 5wt at different temperatures

The dielectric permittivity measurements at microwavefrequencies show the same phenomena The dielectric con-stants measured at several frequencies and at a constanttemperature of 27∘C (300K) are shown in Figure 8

The literature about influence of graphene on themicrowave properties of the elastomeric composites is veryrare The natural rubber [38 39] epoxy [40] or styrene-butadiene rubber based nanocomposites [31] were studied

Figures 9 and 10 present the real and imaginary parts ofthe complex permittivity 120576lowast(120596) = 1205761015840(120596)minus11989412057610158401015840(120596) for a samplewith concentration of filler 5 wt for different temperaturesin which a relaxation process is clearly observed The peakin the imaginary part and the inflection in the real part ofthe complex permittivity do not considerably change withtemperature This behavior is observed for all of the samplesincluding the pure copolymer sample indicating that thisrelaxation process is due to the copolymer chains

Figure 11 presents the Cole-Cole plot of the complexpermittivity for the same sample at different temperaturesThe observed relaxation has a shape of decentered semicircles


08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K

Figure 10 Imaginary part of the complex permittivity for a samplewith concentration 5wt at different temperatures

with their center situated below the abscissa axis for all of thetemperatures and for all of the samples This profile indicatesthat simple exponential decay corresponding to a Debyerelaxation is not appropriate for describing the relaxationphenomenon and should be replaced by an empirical modelsuch as the Cole-Cole model

120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)

In this model which is a modification of the Debye equation120576infin

is the relaxed dielectric constant Δ120576 is the dielectricrelaxation strength (Δ120576 = 120576

0minus 120576infin) 120591 is the relaxation time

and 120572 is a parameter between 0 and 1 that reflects the dipoleinteraction or the complexity of the system The inset ofFigure 11 shows the fit for T = 350K The calculated valuesof 120572 approximately 026 and independent of temperature andfiller concentration show that the system is very complex andfar from the Debye model that corresponds to 120572 = 0 Therelaxation frequency 119891

119903= 12120587120591 can be expressed by the

well-known Arrhenius relation as

119891119903prop exp [minus

119864119886

119896119879] (4)

where 119879 is the absolute temperature and 119896 is the BoltzmannconstantThe activation energy119864

119886 is practically independent

of the filler concentration with a value of 35meV suggestingthat the filler does not interact or only weakly interacts withthe chain segments of the macromolecules in the copolymerFurthermore this result also suggests that there is poorbonding between the polymer matrix and the conductingnanoparticles Stronger interactions between the graphenefiller and polymer matrix should be introduced by surfacemodification of graphene particles [41] which will be the aimof our future research

4 Conclusion

Percolation behavior was observed with a critical concen-tration of approximately 5 wt of conducting filler This

1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K

Figure 11 Cole-Cole plot of the complex permittivity for the samesample with concentration of 5wt at different temperatures Theinset shows the fit

phenomenon could be observed using DC and AC conduc-tivity measurements and was also observed in the dielectricproperties that is in the complex permittivity A relaxationprocess was observed in all of the samples including theneat polymer matrix that is this relaxation is due to thepolymer and not to the fillers The filler slightly changes thisrelaxation but only very weaklyThe activation energy of thisrelaxation process is very lowThe peak in the imaginary partand the inflection in the real part of the complex permittivitydo not considerably change with temperature This resultindicates that the filler does not interact or only weaklyinteracts with the chain segments of the macromolecules inthe copolymer This observation was also confirmed fromthe dynamic mechanical analysis in which an increasingstorage modulus was observed with an increasing amount ofnanofiller but no effect on the tan 120575 curves was observed

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by Bilateral Project SK-PT 0021-10 NMT-ERANET ldquoAPGRAPHELrdquo and by Project VEGA2011912 The authors would like to thank Dr EdmundDobrocka from the Institute of Electrical Engineering SlovakAcademy of Sciences for XRD measurements

References

[1] A K Geim and K S Novoselov ldquoThe rise of graphenerdquo NatureMaterials vol 6 no 3 pp 183ndash191 2007

[2] M S Fuhrer C N Lau and A H MacDonald ldquoGraphenematerially better carbonrdquoMRS Bulletin vol 35 no 4 pp 289ndash295 2010


[3] A H C Neto and K Novoselov ldquoNew directions in science andtechnology two-dimensional crystalsrdquo Reports on Progress inPhysics vol 74 no 8 Article ID 082501 2011

[4] D R Dreyer R S Ruoff andCW Bielawski ldquoFrom conceptionto realization an historial account of graphene and someperspectives for its futurerdquo Angewandte ChemiemdashInternationalEdition vol 49 no 49 pp 9336ndash9344 2010

[5] A H Castro Neto F Guinea N M R Peres K S Novoselovand A K Geim ldquoThe electronic properties of graphenerdquoReviews of Modern Physics vol 81 no 1 pp 109ndash162 2009

[6] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010

[7] X Huang Z Yin S Wu et al ldquoGraphene-based materialssynthesis characterization properties and applicationsrdquo Smallvol 7 no 14 pp 1876ndash1902 2011

[8] X Huang X Qi F Boey and H Zhang ldquoGraphene-basedcompositesrdquo Chemical Society Reviews vol 41 no 2 pp 666ndash686 2012

[9] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010

[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011

[11] Z Spitalsky C A Krontiras S N Georga and C GaliotisldquoEffect of oxidation treatment of multiwalled carbon nanotubeson the mechanical and electrical properties of their epoxy com-positesrdquoComposites Part A Applied Science andManufacturingvol 40 no 6-7 pp 778ndash783 2009

[12] L C Costa M E Achour M P F Graca M El HasnaouiA Outzourhit and A Oueriagli ldquoDielectric properties of theethylene butylacrylatecarbon black nanocompositesrdquo Journalof Non-Crystalline Solids vol 356 no 4-5 pp 270ndash274 2010

[13] M El Hasnaoui M P F Graca M E Achour et al ldquoElectricalproperties of carbon blackcopolymer composites above andbelow themelting temperaturerdquo Journal ofMaterialsamp Environ-mental Science vol 2 no 1 pp 1ndash6 2011

[14] M El Hasnaoui M P F Graca M E Achour and L CCosta ldquoElectric modulus analysis of carbon blackcopolymercomposite materialsrdquo Materials Sciences and Applications vol2 no 10 pp 1421ndash1426 2011

[15] M El Hasnaoui M P F Graca M E Achour et al ldquoEffect oftemperature on the electrical properties of copolymercarbonblack mixturesrdquo Journal of Non-Crystalline Solids vol 356 no31-32 pp 1536ndash1541 2010

[16] I Krupa J Prokes I Krivka and Z Spitalsky ldquoElectri-cally conductive polymer composites and nanocompositesrdquo inHandbook ofMultiphase Polymer Systems A Boudenne L IbosY Candau and S Thomas Eds chapter 11 pp 425ndash477 Wiley2011

[17] S Paszkiewicz A Szymczyk Z Spitalsky et al ldquoElectricalconductivity of poly(ethylene terephthalate)expanded graphitenanocomposites prepared by in situ polymerizationrdquo Journalof Polymer Science Part B Polymer Physics vol 50 no 23 pp1645ndash1652 2012

[18] O Menes M Cano A Benedito et al ldquoThe effect of ultra-thin graphite on the morphology and physical properties ofthermoplastic polyurethane elastomer compositesrdquo CompositesScience and Technology vol 72 no 13 pp 1595ndash1601 2012

[19] J Liang Y Xu Y Huang et al ldquoInfrared-triggered actuatorsfrom graphene-based nanocompositesrdquoThe Journal of PhysicalChemistry C vol 113 no 22 pp 9921ndash9927 2009

[20] J Loomis B King T Burkhead et al ldquoGraphene-nanoplatelet-based photomechanical actuatorsrdquo Nanotechnology vol 23 no4 Article ID 045501 2012

[21] Y R Lee A V Raghu H M Jeong and B K Kim ldquoProper-ties of waterborne polyurethanefunctionalized graphene sheetnanocomposites prepared by an in situ methodrdquoMacromolecu-lar Chemistry and Physics vol 210 no 15 pp 1247ndash1254 2009

[22] D A Nguyen A V Raghu J T Choi and H M Jeong ldquoProp-erties of thermoplastic polyurethanefunctionalised graphenesheet nanocomposites prepared by the in situ polymerisationmethodrdquo Polymersamp Polymer Composites vol 18 no 7 pp 351ndash358 2010

[23] W Zheng X H Lu and S-C Wong ldquoElectrical and mechan-ical properties of expanded graphite-reinforced high-densitypolyethylenerdquo Journal of Applied Polymer Science vol 91 no 5pp 2781ndash2788 2004

[24] D Spasevska G P LealM Fernandez J B GilevM Paulis andR Tomovska ldquoCrosslinked reduced graphene oxidepolymercomposites via in situ synthesis by semicontinuous emulsionpolymerizationrdquo RSC Advances vol 5 no 21 pp 16414ndash164212015

[25] T D Fornes and D R Paul ldquoModeling properties of nylon6clay nanocomposites using composite theoriesrdquo Polymer vol44 no 17 pp 4993ndash5013 2003

[26] P Potschke M Abdel-Goad S Pegel et al ldquoComparisonsamong electrical and rheological properties of melt-mixedcomposites containing various carbon nanostructuresrdquo Journalof Macromolecular Science Part A Pure and Applied Chemistryvol 47 no 1 pp 12ndash19 2010

[27] G Chen W Weng D Wu et al ldquoPreparation and charac-terization of graphite nanosheets from ultrasonic powderingtechniquerdquo Carbon vol 42 no 4 pp 753ndash759 2004

[28] T Ramanathan S Stankovich D A Dikin et al ldquoGraphiticnanofillers in PMMAnanocompositesmdashan investigation of par-ticle size and dispersion and their influence on nanocompositepropertiesrdquo Journal of Polymer Science Part B Polymer Physicsvol 45 no 15 pp 2097ndash2112 2007

[29] L C Costa A Aoujgal M P F Graca et al ldquoMicrowavedielectric properties of the system Ba

1minus119909

Sr119909

TiO3

rdquo Physica BCondensed Matter vol 405 no 17 pp 3741ndash3744 2010

[30] H Li X Zeng and J Guo ldquoEpoxidation of styrene-isoprene-styrene block copolymer and research on its reaction mech-anismrdquo Journal Wuhan University of Technology MaterialsScience Edition vol 25 no 3 pp 403ndash407 2010

[31] B J P Adohi D Bychanok B Haidar and C BrosseauldquoMicrowave and mechanical properties of quartzgraphene-based polymer nanocompositesrdquo Applied Physics Letters vol102 no 7 Article ID 072903 2013

[32] F Henry Developpement de la metrologie hyperfrequences etapplication a lrsquoetude de lrsquohydratation et la diffusion de lrsquoeau dansles materiaux macromoleculaires [PhD thesis] Paris France1961

[33] I Krupa M Prostredny Z Spitalsky J Krajci and M A SAlmaadeed ldquoElectrically conductive composites based on anelastomeric matrix filled with expanded graphite as a potentialoil sensing materialrdquo Smart Materialsampd Structures vol 23 no12 Article ID 125020 2014

[34] Z Sun Y Ma Y Xu et al ldquoEffect of the particle size ofexpandable graphite on the thermal stability flammability and


mechanical properties of high-density polyethyleneethylenevinyl-acetateexpandable graphite compositesrdquo Polymer Engi-neering and Science vol 54 no 5 pp 1162ndash1169 2014

[35] L Peponi A Tercjak R Verdejo M A Lopez-Manchado IMondragon and J M Kenny ldquoConfinement of functionalizedgraphene sheets by triblock copolymersrdquoThe Journal of PhysicalChemistry C vol 113 no 42 pp 17973ndash17978 2009

[36] S Ansari M M Neelanchery and D Ushus ldquoGraphenepoly(styrene-b-isoprene-b-styrene) nanocomposite opticalactuatorsrdquo Journal of Applied Polymer Science vol 130 no 6pp 3902ndash3908 2013

[37] B Li and W-H Zhong ldquoReview on polymergraphite nano-platelet nanocompositesrdquo Journal of Materials Science vol 46no 17 pp 5595ndash5614 2011

[38] O A Al-Hartomy A Al-Ghamdi N Dishovsky et alldquoDielectric and microwave properties of natural rubber basednanocomposites containing graphenerdquo Materials Sciences andApplications vol 3 pp 453ndash459 2012

[39] O A Al-Hartomy A A Al-Ghamdi F Al-Salamy et alldquoDielectric andmicrowave properties of graphene nanoplateletscarbon black filled natural rubber compositesrdquo InternationalJournal of Materials and Chemistry vol 2 no 3 pp 116ndash1222012

[40] GDe Bellis IMDeRosa A DinescuM S Sarto andA Tam-burran ldquoElectromagnetic absorbing nanocomposites includingcarbon fibers nanotubes and graphene nanoplateletsrdquo in Pro-ceedings of the IEEE International Symposium on Electromag-netic Compatibility (EMC rsquo10) pp 202ndash207 Fort Lauderdale FlaUSA July 2010

[41] Z Spitalsky M Danko and J Mosnacek ldquoPreparation offunctionalized graphene sheetsrdquo Current Organic Chemistryvol 15 no 8 pp 1133ndash1150 2011

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


improvement in themodulusThe observed reinforcing effectwas attributed to the improved interactions obtained duringthis in situ method [21] Similar results were also obtained inthe thermoplastic polyurethane matrix [22] however only aweak reinforcement effect has been reported in polyethylenematric [23]Thephysical properties of the grapheme-polymercomposites depend also highly on the degree of cross-linkingand the finalmorphology [24]This result can be attributed tothe decreased aspect ratio of the filler as it can emerge eitherin a wrinkled conformation of the filler [25] or due to particleattrition during mixing [26] It was also reported that thesonication of expanded graphite in a viscous solution enablesthe further separation of graphene platelets into smallernanometer-sized platelets [27] As the expanded graphenelayers are intercalated by polymer chains it is hypothesizedthat the sonicated expanded graphene possesses a largernumber of smaller platelets and therefore serves as a moreefficient nanofiller [28]

The need to protect electronic components againstelectromagnetic interference is very important particularlyat microwave frequencies where wireless communicationsoccur The effects of electromagnetic interference can bedecreased by positioning a shielding material between thesource of the electromagnetic field and the electronic compo-nent Graphene composites are a good possibility for achiev-ing that objectiveThenmicrowave dielectric properties weremeasured using the resonant cavity method [29 30] To thebest of our knowledge there is only one work concerningmicrowave spectroscopy study of graphene-based elastomercomposite materials when the microwave permittivity ofstyrene-butadiene rubber composite was unaffected by strainup to 8 [31]

Therefore in this study expanded graphite obtainedusing the solution sonication techniquewas employed In thispaper the results from a study on the molecular dynamics ofa styrene-isoprene-styrene and graphene sheet composite arepresented The composites were prepared using the solutiontechnique and their percolation behaviors impedance spec-tra and mechanical properties were characterized

2 Materials and Methods

21 Materials GFG50 expanded graphite particles withan average size of 50 120583m were obtained from SGL Tech-nologies GmbH Germany Kraton D1165 PT (a linear tri-block copolymer based on styrene and isoprene with apolystyrene content of 30) was purchased from KratonPerformance Polymers Inc Toluene with a pa purity waspurchased from Sigma-Aldrich and was used without furtherpurification

A dispersion of GFG50 in 50mL of toluene was producedby sonication in an ultrasonic bath for 20 minutes followedby mixing with a polymer solution (2 g of polymer wasdissolved in 20mL of toluene under rigorous stirring) Thethin films were casted onto a Teflon array The thin filmswith a nanofiller concentration of up to 10wt exhibited anaverage thickness of approximately 400 120583m

22 Polymer Characterization XRD analysis was conductedusing a Bruker D8 DISCOVER diffractometer equipped withanX-ray tubewith a rotatingCu anode operating at 12 kWAllof the measurements were performed using a parallel beamgeometry with a parabolic Goebel mirror positioned in theprimary beam

The X-ray diffraction patterns were recorded using agrazing incidence setup with an angle of incidence 2∘ Thesurface morphologies were examined using scanning elec-tron microscopy with a dual beam (FIBSEM) MicroscopeQuanta 3D 200i (FEI)The free surface and the cross sectionsof thesematerials were investigatedAll of the specimensweresputter coated with a thin layer of gold prior to examination

TGA measurements were performed using a MettlerToledo TGASDTA 851 instrument in a nitrogen flow(30mLmin) using a heating rate of 10∘Cmin over the tem-perature range from 25∘C to 800∘C Indium and aluminumwere used for temperature calibrationThe amount of sampleused was 2mg Two parallel runs were performed for eachsample

Viscoelastic measurements were performed using a TAInstruments DMAQ800 dynamicmechanical analyzer Sam-ples with uniform shapes were measured in the moduletensile multifrequency strain at 10Hz and a strain amplitudeof 5 120583m The loss tangent (tan 120575) and storage modulus wereobtained from minus100∘C to 130∘C using a heating rate of2∘Cmin

For the electrical measurements of the samples contactswere made by painting both sides of the polymer samplewith silver paste simulating a parallel plate capacitor witha surface area of 1 cm2 and a distance between electrodes ofapproximately 04mm

DC conductivity measurements were conducted usingthe standard two contacts with the guard method using aKeithley 617 Electrometer at temperatures between minus110∘Cand 90∘C in an inert atmosphere

Dielectric measurements were performed using an Agi-lent 4294A Precision Impedance Analyzer for frequenciesbetween 40Hz and 2MHz The general approach is to applyan electrical stimulus and to observe the response of themate-rial It is then assumed that the properties of the electrode-material system are time invariant which is an importantassumption for the measurement method The amplitudeof the applied voltage was 1 V From a practical point ofview dielectric spectroscopy can provide a measurementof the complex permittivity 120576lowast(120596) = 1205761015840(120596) minus 11989412057610158401015840(120596) orderived quantities related to it such as the dielectricmodulus119872 = 120576

minus1 The macroscopic properties such as impedance119885lowast

(120596) = 1198851015840

(120596) minus 11989411988510158401015840

(120596) or admittance 119884 = 119885minus1 canalso be obtained The interrelations between these quantitiesare simple when their geometric parameters (shape size andthickness) are known In our case the measured values wereused to calculate the dielectric complex modulus (119872lowast) usinga parallel RC (Resistance-Capacitor) model of the sampleThe estimated relative errors on both the real and imaginaryparts of the complex permittivity were less than 2

For the microwave dielectric measurements the resonantcavity method at 27 GHz was used The samples used were


Inte

nsity

10 20 30 40 50 60

2120579 (∘)

10

5

050



1205761015840

= 119870Δ119891

1198910

119881

V+ 1

12057610158401015840

=119870

2Δ(

1119876)119881

V

(1)


0is the













(a) (b)

(c)


110

100

90

80

70

60

50

40

30

20

10

0

0 100 200 300 400 500 600 700 800

T (∘C)

Wei

ght l

oss (

)

005124

56810




119909 1198791198921

by tan 120575 (∘C) SD 1198791198922


1015840



2500

2000

1500

1000

500

0

Stor

age m

odul

us (M

Pa)

minus100 minus50 0 50 100 150

Temperature (∘C)

15

10

05

00ta

n 120575





001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

1E minus 12

0 2 4 6 8 10

Concentration (wt)

120590D

C(S

mminus1)




0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE


001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)




Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)


60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)


16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K







08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Inte

nsity

10 20 30 40 50 60

2120579 (∘)

10

5

050



1205761015840

= 119870Δ119891

1198910

119881

V+ 1

12057610158401015840

=119870

2Δ(

1119876)119881

V

(1)


0is the













(a) (b)

(c)


110

100

90

80

70

60

50

40

30

20

10

0

0 100 200 300 400 500 600 700 800

T (∘C)

Wei

ght l

oss (

)

005124

56810




119909 1198791198921

by tan 120575 (∘C) SD 1198791198922


1015840



2500

2000

1500

1000

500

0

Stor

age m

odul

us (M

Pa)

minus100 minus50 0 50 100 150

Temperature (∘C)

15

10

05

00ta

n 120575





001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

1E minus 12

0 2 4 6 8 10

Concentration (wt)

120590D

C(S

mminus1)




0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE


001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)




Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)


60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)


16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K







08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c)


110

100

90

80

70

60

50

40

30

20

10

0

0 100 200 300 400 500 600 700 800

T (∘C)

Wei

ght l

oss (

)

005124

56810




119909 1198791198921

by tan 120575 (∘C) SD 1198791198922


1015840



2500

2000

1500

1000

500

0

Stor

age m

odul

us (M

Pa)

minus100 minus50 0 50 100 150

Temperature (∘C)

15

10

05

00ta

n 120575





001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

1E minus 12

0 2 4 6 8 10

Concentration (wt)

120590D

C(S

mminus1)




0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE


001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)




Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)


60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)


16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K







08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





119909 1198791198921

by tan 120575 (∘C) SD 1198791198922


1015840



2500

2000

1500

1000

500

0

Stor

age m

odul

us (M

Pa)

minus100 minus50 0 50 100 150

Temperature (∘C)

15

10

05

00ta

n 120575





001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

1E minus 12

0 2 4 6 8 10

Concentration (wt)

120590D

C(S

mminus1)




0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE


001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)




Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)


60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)


16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K







08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0012

0008

0004

0000

Tran

smiss

ion

(au

)

2778 2780 2782 2784

times109

Frequency (Hz)

x = 1

x = 4

x = 5

Empty

PTFE


001

1E minus 4

1E minus 6

1E minus 8

1E minus 10

0 2 4 6 8 10 12

Concentration (wt)

200

160

120

80

40

0

120590M

W(S

mminus1)

120590D

C(S

mminus1)




Using the relation

120590AC = 1205761015840101584021205871198911205760 (2)


60

40

20

0

200

150

100

50

0

120576998400(2

7G

Hz)

120576998400(1

kHz

1M

Hz)

0 2 4 6 8 10

Concentration (wt)


16

14

12

10

120576998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K







08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




08

06

04

02

00

120576998400998400

102

103

104

105

106

Frequency (Hz)

T = 350K

+50K

T = 200 K



120576lowast

(120596) = 120576infin+Δ120576

1 + (119894120596120591)1minus120572 (3)








119864119886

119896119879] (4)




4 Conclusion


1

0

3

2

1

0

11 12

12

13

13

14

14

15

15

120576998400

120576998400

120576998400998400

120576998400998400

T = 200 K

T = 350K





Acknowledgments


References































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials































1minus119909

Sr119909

TiO3























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article mechanical and electrical properties of

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