research article electrical and thermal characterization

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013, Article ID 160931, 9 pageshttp://dx.doi.org/10.1155/2013/160931

Research ArticleElectrical and Thermal Characterization of Electrospun PVPNanocomposite Fibers

Waseem S. Khan,1 Ramazan Asmatulu,1 and Mohamed M. Eltabey2,3

1 Department of Mechanical Engineering, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0133, USA2 Basic Engineering Science Department, Faculty of Engineering, Menoufiya University, Shebin El-Kom, Egypt3Medical Physics Department, Faculty of Medicine, Jazan University, Saudi Arabia

Correspondence should be addressed to Ramazan Asmatulu; [email protected]

Received 30 October 2012; Revised 30 January 2013; Accepted 6 February 2013

Academic Editor: Theodorian Borca-Tasciuc

Copyright © 2013 Waseem S. Khan 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.

Polyvinylpyrrolidone (PVP) solutions incorporated with multiwall carbon nanotubes (MWCNTs) were electrospun at variousweight percentages, and then the electrical resistance and some thermal properties of these nanocomposite fibers were determinedusing a high-accuracy electrical resistance measurement device. During the electrospinning process, system and processparameters, such as concentrations, applied voltage, tip-to-collector distance, and pump speeds, were optimized to receive theconsistent nanocomposite fibers. When polymers are used in many industrial applications, they require high electrical and thermalconductivities. Most polymers exhibit low electrical conductivity values; however, in the presence of conductive inclusions, theelectrical resistance of theMWCNTfibers was reduced from 50MΩ to below 5MΩ, whichmay be attributed to the higher electricalconductivities of these nanoscale inclusions and fewer voids under the applied loads. This study may open up new possibilities inthe field for developing electrically conductive novel nanomaterials and devices for various scientific and technological applications.

1. Introduction

1.1. General Background. Electrospinning is a versatilemethod to produce ultrafine polymeric fibers. It hasattracted enormous attention due to the numerous optionsfor fabricating ultrafine fibers [1]. When the diametersof polymer are reduced to the nanoscale, some exoticcharacteristics appear, such as high surface area-to-volumeratios, mechanical flexibility, and superior mechanicalproperties, compared to their bulk-size counterparts [2].During electrospinning, a high voltage and consequentlyhigh electrostatic field are applied to a polymer solution atthe end of a capillary tube. The electrostatic field introducescharges in the solution when the mutual repulsions betweencharges reach a threshold value, and a fluid jet forms aconical droplet at the tip of a capillary tube, resulting in theformation of a Taylor cone [3, 4]. The jet travels in a straightpath, called the jet’s length, experiences bending instabilitiesto form spiral motions, and finally is collected on a screen,

which is either grounded or connected to a DC supply ofopposite polarity. Figure 1 shows a general schematic view ofthe electrospinning process.

Parameters such as load, temperature, and inclusionhave a direct relationship to the electrical and thermalresistances of the modified fibers. When the load is appliedon a film of the fibers, individual fibers and molecules ofpolymer move closer together where the heat conductionbecomes easier, and electrical resistance is reduced drasticallydue to the lower separation distances, higher number ofcharge carrier/holes (free mobile particles carrying electricalcharges), and polarizability. The increase in mobility of thecharge carriers with temperature is governed by the followingArrhenius dependent equation [5, 6]:

𝜇𝑡= 𝜇𝑜𝑒(−𝐸𝜇/𝑅𝑇), (1)

where 𝜇𝑡is the mobility at temperature 𝑇(∘K), 𝐸

𝜇is the

activation energy, 𝑅 is Boltzmann’s constant, and 𝜇0is a

2 Journal of Nanomaterials

Syringe pumpPolymersolution Needle

Collector

Connection wire

GroundElectrospun fibers

DC power supply

Highvoltage

Figure 1: Schematic view of an electrospinning process.

temperature-independent constant. The basic expression forthe electrical conductivity,𝐾

𝑝, is [7]

𝐾𝜌= ∑𝑛

𝑖𝑒𝑖𝜇𝑖, (2)

where 𝑛𝑖is the density of the charge carriers, and 𝑒

𝑖and 𝜇

𝑖

are the corresponding charges and mobility of the chargecarriers, respectively. The factors that mainly influence theelectrical resistance of nanocomposite fibers under load andtemperature are related to the hysteresis effects, charge car-rier concentration, polarizability, and porosity/void. Whenmultiwall carbon nanotubes (MWCNTs) are added intopolymers, the charge carrier concentration increases, as doesthe conduction rate. At higher temperatures, the mobilityof the charge carriers increases and, likewise, the conduc-tion. Increasing the wt% of MWCNTs increases the dipolemoments in the polymer, which in turn enhances the polar-izability of the materials and thereby conduction. Porosity isthe amount of voids or empty spaces presented in a material.This is an important physical property that affects almost allphysical properties of the material. The dynamic lag betweeninput and output is commonly referred to as hysteresis, orrate-dependent hysteresis. This effect is generally observedduring the unloading of a material after applying tensilestresses. This phenomenon is common in ductile materials,such as rubber and plastic. The percolation behavior of anelectrical conduction in nanotubes-polymer composites in abulk and thin filmhas been extensively studied formany years[8]. The high aspect ratio of CNTs is beneficial in makingpercolation network at lower loading of the inclusions.

There are some other studies on the nanotubes-basedpolymeric electrospun nanocomposite fibers for variouspurposes [9–13]. A detailed study of the electrical andthermal properties of electrospun fibers was presented in ourstudy. Thermal analysis is an important analytical techniquefor understanding the structural/property relationship ofa polymeric material, and it is also a helpful method todetermine the thermal stability of the materials [9]. Differ-ential scanning calorimetry is a technique to characterizethe thermal stability of a polymer. DCS determines the

heat flow rate associated with thermal changes that canbe measured as a function of temperature and time. DSCtechnique can also be used to study the melting behaviorand phase transition of the materials. The objective of thiswork was to study the electrical transport properties andthermal stability of nanotubes-based polymeric fibers. Thestudy of variation of the temperature dependent electricalconduction of nanocomposite fibers can provide an insightinto the mechanism of charge and heath transport [8].

The nanophase/nanoize materials that serve as fillers inthe polymeric matrices are the clusters of atoms or moleculeshaving size dependent properties, which are different fromtheir bulk counterparts [10]. Polymer nanocomposites areof great importance due to their novel properties resultingfrom the excellent combination of parents constituents into asingle phase [11]. Polymer nanocomposites have been findingextensive applications owing to their easy processing, lowmanufacturing cost, and unique physicochemical properties[12]. Electrospinning is a rapid, easy and low cost process formany industrial applications [13].

1.2. Polymer Nanocomposites. Polymer-carbon nanotube(CNT) composites have recently attracted a considerableamount of scientific interest because of their structuralcharacteristics, such as high aspect ratio, surface area, andelectrical, thermal, and mechanical properties, all of whichare positive signs for the fabrication of ultralightweightand robust composites [14]. The biggest challenge infabricating such composites is the uniform dispersion ofCNTs in a polymer matrix, since van der Waals forcesbetween individual nanotubes cause agglomeration, whichreduces the expected properties of nanocomposites [14].A good dispersion technique is essential for allowing theformation of an interconnecting filler network of CNTsat a lower concentration without changing the electricalresistivity. CNTs can provide electrical conduction atlower concentrations in the nanocomposite structure. Thisproperty is required in commercial applications to dissipateelectrostatic charge and thermal heat [14]. In the presentstudy, in order for CNTs to retain their properties, CNTs werephysically dispersed in a polymer matrix instead of grafting.

Journal of Nanomaterials 3

(a) (b)

(c) (d)

Figure 2: SEM images of PVP nanocomposite fibers incorporated with the following wt% MWCNTs: (a) 0, (b) 0.5, (c) 1, and (d) 2.Electrospinning experiments conducted at 85 : 15 PVP and ethanol ratio, 25 kV DC voltage, 20 cm separation distance, and 2mL/hr pumpspeed.

2. Experimental

2.1. Materials. Polyvinylpyrrolidone (PVP) with a molecularweight of 130,000 g/mole was purchased from the Sigma-Aldrich company. Multiwall carbon nanotubes with a diam-eter of 140 ± 30 nm and a length of 7 ± 2 microns werepurchased from the Fisher Scientific company. Different wt%(0, 1, 2, and 4) of MWCNTs was mechanically dispersed inethanol, and PVP polymer in granular form was added to thedispersion prior to the 30-minute sonication. The dispersionwas constantly stirred at 60∘C for 12 hours before the elec-trospinning process. Special care was taken to disperse theMWCNTs uniformly; otherwise, the electrospinning processand/or nanocomposite fiber morphology would deteriorate.

2.2. Methods. The prepared dispersion was transferred to a10mL plastic syringe connected to a capillary needle withan inside diameter of 0.3mm. A platinum electrode insidethe syringe was attached to a high DC voltage supply. In thisstudy, the applied voltage (18–20 kV), the syringe pump speed(1–3mL/hr), and the distance between capillary tube andgrounded counter electrode (15–25 cm) were tested to opti-mize the electrospinning parameters. The grounded counterelectrode was a flat aluminum foil placed at a distance of 15–25 cm from the capillary tube. Electrospun fibers were thencollected on a grounded screen and dried in an oven at 60∘Cfor 6 to 8 hours to remove all residual solvents. A scanningelectron microscope (SEM) (JEOL Model JSM-6460LV) was

used to identify the morphology and surface characteristicsof the nanocomposite fibers. Figure 2 shows the selectedSEM images of the PVP electrospun nanocomposite fibers. Acommercial differential scanning calorimeter (DSC) (modelQ1000) was used to measure the glass transition temperature(𝑇𝑔), heat flow, and heat flow derivative of the specimens.

Dry nitrogen gas was purged through the DSC cell duringthe experiments, each of which had 10mg of samples inan aluminum hermetic pan. During the tests, samples wereheated from 0∘C to 300∘C at the rate of 20∘C/min.

A homemade electrical resistance device was built, testedon the known thin films, and then used for the electricalcharacterizations of the electrospun nanocomposite fibers[4]. A thin film of the fibers was positioned between twocylinders (2.5 cm in diameter) of a hydraulic press on whichtwo probes of a highly sensitive multimeter were placed torecord the electrical resistance values of the samples. A thincoating of a conductive paste was applied on cylinders inorder to avoid contact resistance. The applied loads werevaried from 0 to 9 tons (0–1440 kg/cm2) during the resistancemeasurements. Each sample was externally loaded 3–5 timesand the resistance changes recorded.

3. Results and Discussion

3.1. Loads versus Electrical Resistance of PVP Fibers. In eachtest, the same nanocomposite fiber films were externallyloaded five times during the measurements. Figure 3 shows


0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

70

80

90

Load (ton)

1st load2nd load3rd load

4th load

Resis

tanc

e (M

Ω)

(a)

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10Load (ton)

5th load1st load2nd load3rd load

4th load

Resis

tanc

e (M

Ω)

(b)

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

70

80

90

Load (ton)


4th load

Resis

tanc

e (M

Ω)

(c)

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10Load (ton)


4th load

Resis

tanc

e (M

Ω)

(d)

Figure 3: Load versus electrical resistance curves of PVP nanocomposite fibers obtained at following wt% MWCNTs: (a) 0, (b) 1, (c) 2, and(d) 4.

the load versus electrical resistance values of the PVPnanocomposite fibers at various percentages of MWCNTs.As expected, resistance decreases with the applied load forall tested samples. This behavior may be explained using thefollowing equation [15]:

𝑅resistance = 𝜌(𝐿

𝐴) , (3)

where 𝜌, 𝐿, and 𝐴 are resistivity, thickness, and cross-sectional area of the sample, respectively. When the load isincreased on nanocomposite fibers, two major changes inthickness and porosity can be observed on the samples. Thethickness of the sample decreases under the load, and thecontact area between the fibers and electrode increases, which

in turn reduces the overall electrical resistance. At 0wt%of MWCNTs (Figure 3(a)), the resistance increases in eachtrial when the load is removed, which may be attributedto the hysteresis and porosity changes, whereas at 1 and2wt% MWCNTs (Figures 3(b) and 3(c)), the porosity of thefiber film is likely to be reduced because of the conductivenanoscale inclusions. Resistance increases only in the firsttrial after unloading, and in subsequent trials, the resistancecurves overlapped due to the higher wt% ofMWCNTs, whichis expected to reduce the porosity and electrical resistance ofnanocomposite fibers significantly.

At a higher loading of MWCNTs, the resistance curves(Figure 3(d)) overlap each other, which may be due to thefact that at high loading, polarizability and charge carrier


0

20

40

60

80

100

290 300 310 320 330 340 350 360 370 380 390 400

PVP with 0% MWCNTs PVP with 1% MWCNTs

PVP with 2% MWCNTsPVP with 4% MWCNTs

Temperature (∘K)

Resis

tanc

e (Ω·m

)

Figure 4: Temperature versus electrical resistance curves of PVPnanocomposite fibers obtained at 0, 1, 2, and 4wt% MWCNTs.

concentrations of the nanocomposite fibers are alsoincreased. Adding MWCNTs into the polymeric fibersincreases both the electrical and thermal conductivities ofthe fibers [4]. At higher MWCNTs, there is no shift betweensuccessive trials, since MWCNTs make a nanocompositeconductive enough to reduce the electrical resistance. Atlower MWCNT contents, possibly the proper percolatingnetwork structure was not established, and therefore, theresistivity remained high [16]. However, when the wt.% ofMWCNTs reached at 4%, a continuous nanotube networkwas established to significantly drop the electrical resistance.For example, the resistance of pure PVP fiber was 50MΩ,which was reduced to 30MΩ at 4wt.% of MWCNTs withoutany loading. Once the network of MWCNTs is established,a pathway is created to support the electron transportationprocess among carbon nanotubes [17]. Zhu et al. [17]established a relationship between the aspect ratio (L/r),where L and r are the length and radius of an individualnanofiber and percolation threshold (Pc). The aspect ratio ofMWCNTs used in this study is 100.The percolation thresholdwas established at 4wt% of MWCNTs, indicating a highaspect ratio of the nanocomposite fibers.

3.2. Temperature versus Electrical Resistance of PVP Fibers.Figure 4 shows the effects of temperatures on the electricalresistance of nanocomposite fibers at a constant loading. AK-Type thermocouple was attached on the top surface of thefiber for recording temperature readings, while two probesof a multimeter were attached on either side of the film ofthe fibers to record electrical resistance. The whole assemblywas enclosed in glass fiber insulation in order to avoidthermal losses. As shown in Figure 4, increasing the sampletemperature drastically reduced the electrical resistance. Therelation between temperature and resistivitymay be governed

by the following Arrhenius dependent equation [6, 7, 14, 15,18]:

𝜌 = 𝜌0𝑒(𝐸𝜇/𝑅𝑇), (4)

where 𝜌 is the resistivity at temperature 𝑇(𝐾), 𝐸𝜇is the

conduction activation energy, 𝑅 is the Boltzmann’s constant,and 𝜌

0is the temperature-independent constant. As the

temperature increases, themolecules undergo a phase change(e.g., rubbery and partly solid) and likely slide over eachother to facilitate the electrical conductions. This drasti-cally decreases the overall electrical resistances of the fibers(Figure 4).

There is a close correlation among the conductivity, aspectratio, concentration, and dispersion of CNTs filler materials,all of which influence the particle-particle and particle-matrix interactions [19]. The existence of conductivity canbe attributed to the formation of conductive pathways, whenthe wt% ofMWCNTs exceeds a critical proportion, called thepercolation threshold. At a low percentage of MWCNTs, thedistance between particles (MWCNTs) is large, resulting in alower conductivity.The percolation threshold exists at highernanoscale inclusions, and in the absence of a conductivepathway, the polymeric materials are mostly called insulators[16, 19, 20]. At a high percentage of MWCNTs, the MWC-NTs tend to agglomerate due to the lack of the dispersionand interfacial interactions, and subsequently impede theformation of conductive pathways [19]. Therefore, a gooddispersion is necessary to establish the conductive pathwayin the nanocomposite fibers.

Phonon conduction by a percolated network ofMWCNTsleads to an increase in thermal and electrical conductivity byseveral order of magnitudes when the required filler contentis reached to establish percolation threshold [20]. The perco-lation threshold decreases with increasing aspect ratio of fillermaterial present in the polymer matrix [21]. CNTs provideelectrical conduction when incorporated into the polymermatrix. Test results showed that a small concentration ofCNTs would be needed to obtain relatively high electricalconductions, which is useful in a wide range of industrialapplications [22]. Electron transport in composites usuallyinvolves thermally activated transport through the networkof charge carriers between nearest-neighbor particles at closeproximity forming an overlap of electron wave function ofeach particle [21]. The formation of a MWCNT conductionpathway allows the electrons to travel through the compositestructure of the fibers. The MWCNTs consist of concentricmultiwalled tubes with one end capped; therefore, only theouter layer contributes to the electron transfer that gives thenanocomposites their electrical properties [23].

Since the mechanism of heating the polymer aboveroom temperature is thermally induced, the resistance versustemperature behavior may be understood by the activationenergy values of the nanocomposite fibers. Figure 5 showsthe plot of the Log𝑅 and 1000/T at 0, 1, 2, and 4wt%of MWNTs. This plot shows a linear behavior and can bedivided into three distinct zones, indicated by green, blue, andred lines. The second zone shows the exponential function,which clearly indicates that the thermal process follows the


2.4 2.6 2.8 3 3.2 3.4

0

0.5

1

1.5

2

2.5

−0.5

PVP with 0% MWCNTs

∼33∘C

∼64∘C

Log 𝑅

1000/𝑇 (∘K−1)

(a)

2.7 2.8 2.9 3 3.1 3.2 3.3 3.4

0

0.5

1

1.5

2

−0.5

−1

PVP with 1% MWCNTs

∼38∘C

∼49∘C

1000/𝑇 (∘K−1)

Log 𝑅

(b)

0

0.5

1

1.5

2

−0.5

−1

2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4

PVP with 2% MWCNTs

∼38∘C

48∘C

Log 𝑅

1000/𝑇 (∘K−1)

(c)

0

0.5

1

1.5

2

−0.5

−1.5

−1

37∘C

50∘C

2.7 2.8 2.9 3 3.1 3.2 3.3 3.4

PVP with 4% MWCNTs

1000/𝑇 (∘K−1)

Log 𝑅

(d)

Figure 5: Log𝑅 versus 1000/T curves of PVP nanocomposite fibers obtained at various wt% MWCNT inclusions: (a) 0, (b) 1, (c) 2, and (d)4 wt%.

Arrhenius equation.The activation energy of the electrospunPVP/MWCNT composite is influenced by the reinforcementeffect of nanotubes, increased cross-linking density, andrestrictedmobility of the polymer and nanotube interactions.

Figure 6 is the Log𝑅 versus 1/T plot for 0, 2, and 4wt%of MWCNTs in PVP polymer. This plot shows a linearrelationship between the Log𝑅 and 1/T, indicating a goodfit for the Arrhenius equation. From Figure 6, the activationenergy values were calculated as 48.37 KJ/mole (0.50 eV),62.88KJ/mole (0.65 eV), and 76.96KJ/mole (0.79 eV) for 0,2, and 4wt% of MWCNTs in PVP nanocomposite fibers,respectively. Results also indicate that themobility of the PVPchain in an amorphous region was restricted by the presenceof the nanotubes [24–28].Thatmay be the possible reason for

why activation energies were increased as the wt% of high-modulusMWCNTs increased.When the polymer is strained,it must overcome the energy barrier in order to allow thepolymer chains to move around and rotate the chain bonds.Thus, this energy barrier may be the activation energy of thepolymeric system [29].

Figure 7 shows the heat flow and heat flow derivativeval-ues. The derivative of the heat flow shows a phase transition,which is a second order and takes place in the temperaturerange of 37∘C to 60∘C. In the presence of MWCNTs, the heatflow decreases as the wt% of MWCNTs increases because ofthe inclusion properties (Figure 7).The thermal conductivityof MWCNTs used in this study is 1600w/m∘K, which is 3 to4 times higher than most common metals. The addition of


0.00308 0.00312 0.00316 0.0032 0.00324

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

PVP with 0 wt.% MWCNTsPVP with 2 wt.% MWCNTsPVP with 4 wt.% MWCNTs

𝑌=9260.7𝑋−28.933

𝑌=7563.1𝑋−23.46

𝑌=5818.2𝑋− 17.271

−0.2

1/𝑇 (∘K)

Log 𝑅

Figure 6: Log𝑅 versus 1/T curves of PVP nanocomposite fibersobtained at 0wt%, 2, wt%, and 4wt% MWCNT inclusions.

0 20 40 60 80 100 120

Hea

t flow

(W/g

)

Zero CNT

Deriv. heat flow

0

0

0

−0.6−6

−8

−12

−6

−12

−16−0.6

−0.9

−0.9

−0.75

−0.75

−0.75

−0.9

Heat flowTemprature (∘C)

4% CNT

1% CNT

Der

iv. h

eat fl

ow (W

/g∘C)

×10−4

Figure 7:Heat flowandheat flowderivative of nanocomposite fibersincorporated with 0wt%, 1 wt%, and 4wt% MWCNTs.

MWCNTs makes the conduction process easier, owing to theincreased polarizability values of the nanocomposite fibers.

3.3. DSC Analysis of PVP Nanocomposite Fibers. Figure 8shows the DSC analysis of the PVP nanocomposite fibersas a function of MWCNT concentrations. PVP is mostlyan amorphous polymer that can undergo a transition phasewhen heated or cooled at a specific temperature, known asthe glass transition temperature (𝑇

𝑔), where the polymer is

in partly a rubbery and partly a glassy phase. It is related tothe segment movement/vibration of the polymer chains. 𝑇

𝑔

is a main function of molecular architecture, monomer units,presence of impurities, nanoscale inclusions, crystallinity,

Hea

t flow

(W/g

)

046.37∘C (H)

Exp up0 50 100 150 200 250 300

−2

−4

−6

−8

−10

218.76∘C

Temperature (∘C)

214.2∘C

298.4 J/g

(a)

218.98∘C

Hea

t flow

(W/g

)

2

0

Exp up0 50 100 150 200 250 300

−2

−4

−6

−8222.52

∘C

Temperature (∘C)

44.39∘C (H) 276.3 J/g

(b)

Figure 8: DCS analysis of PVP nanocomposite fibers associatedwith (a) 0wt% and (b) 4wt% of MWCNTs.

molecular weight, and the rate of temperature changes [24–27]. This transition temperature has been extensively studiedfor many polymers since it is one of the most fundamentalfeatures of polymers. In general, the nanoscale inclusionsdirectly affect the 𝑇

𝑔of the polymeric nanocomposites, and

the interaction of the polymer chains with the surface ofthe inclusion can significantly alter the chain kinetics of theregion that is surrounded by the nanoscale inclusions.

A recent study has shown that nanoscale inclusions inpolymers had no significant effects on the glass transitiontemperature of polymers and polymeric nanocomposites.However, no coherent conclusion has been drawn about theeffect of nanoscale inclusions on the 𝑇

𝑔. Strong interactions

and possible covalent bonding between nanotubes and poly-mer matrix most likely result in an increase in 𝑇

𝑔[24].

Our study also showed that there was no significant effecton the 𝑇

𝑔(from 46.4∘C to 44.4∘C at 4wt%) of PVP fibers

incorporated with MWCNT inclusions (Figure 8). This maybe attributed to the lack of strong covalent bonds betweentheMWCNTs and the polymermatrix.The only considerablechange we found was the heat of the fusion. For example, the


heat of the fusion decreased from 298.4 J/g to 276.3 J/g whenthe inclusion concentration increased from 0 to 4wt%.

4. Conclusions

In the present study, the effects of external loads and temper-atures on the resistance of electrospun polyvinylpyrrolidonenanocomposite fibers were investigated in detail. Thosefactors that influence the resistance are mainly porosity,charge carrier concentration, and polarizability of inclusionsin the polymer matrix. The addition of multiwall carbonnanotubes most likely increased the charge carrier concen-tration and polarizability and reduced the porosity of theelectrospun fiber films under the load. In the load versustemperature experiment, the electrical resistance decreasesbecause the polymer molecules undergo a transition phasein the temperature range of 37∘C to 60∘C. This transitionphase was confirmed by differential scanning calorimetrystudies. No significant effect was observed on the glasstransition temperature property of the PVP nanocompositefibers in the presence of MWCNTs, which may suggest thatno significant covalent bonds existed between the MWCNTsand the polymer matrix.

Acknowledgment

The authors would like to acknowledge the Wichita StateUniversity for the financial and technical support of thiswork.

References

[1] A. Stoiljkovic,M. Ishaque, U. Justus et al., “Preparation of water-stable submicron fibers from aqueous latex dispersion of water-insoluble polymers by electrospinning,” Polymer, vol. 48, no. 14,pp. 3974–3981, 2007.

[2] Z. M. Huang, Y. Z. Zhang, M. Kotaki, and S. Ramakrishna,“A review on polymer nanofibers by electrospinning and theirapplications in nanocomposites,” Composites Science and Tech-nology, vol. 63, no. 15, pp. 2223–2253, 2003.

[3] P. R. Kumar, N. Khan, S. Vivekanandhan, N. Satyanarayana, A.K. Mohanty, andM. Misra, “Nanofibers: effective generation byelectrospinning and their applications,” Journal of Nanoscienceand Nanotechnology, vol. 12, no. 1, pp. 1–25, 2012.

[4] W. S. Khan, Fabrication and characterization of polyvinylpyrroli-done and polyacrylonitrile electrospun nanocomposite fibers[Ph.D. thesis], Wichita State University, Wichita, Kan, USA,2010.

[5] P. P. llich, Selected Problems in Physical Chemistry-Strategies andInterpretations, Springer, New York, NY, USA, 2010.

[6] A. K. Galwey and M. E. Brown, “Application of the arrheniusequation to solid state kinetics: can this be justified?” Ther-mochimica Acta, vol. 386, no. 1, pp. 91–98, 2002.

[7] J. J. O’Dwyer, The Theory of Electrical Conduction and Break-down in Solid Dielectrics, Clarendon Press, Oxford, UK, 1973.

[8] B. Sundaray, Preparation and characterization of electrospunfibers of carbonnanotube- polymerNanocomposite [Ph.D. thesis],Department of Physic, Indian Institute of Technology, Madras,India, 2006.

[9] X. Zhang, Y. Li, G. Lv, Y. Zuo, and Y. Mu, “Thermal and crys-tallization studies of nano-hydroxyapatite reinforced polyamide66 biocomposites,” Polymer Degradation and Stability, vol. 91,no. 5, pp. 1202–1207, 2006.

[10] X. Chen, S. Wei, C. Gunesoglu et al., “Electrospun magneticfibrillar polystyrene nanocomposites reinforced with nickelnanoparticles,”Macromolecular Chemistry and Physics, vol. 211,no. 16, pp. 1775–1783, 2010.

[11] J. Zhu, S. Wei, R. Patil et al., “Ionic liquid assisted electro-spinning of quantum dots/elastomer composite nanofibers,”Polymer, vol. 52, no. 9, pp. 1954–1962, 2011.

[12] D. Zhang, A. B. Karki, D. Rutman et al., “Electrospun polyacry-lonitrile nanocomposite fibers reinforced with Fe3O4 nanopar-ticles: fabrication and property analysis,” Polymer, vol. 50, no. 17,pp. 4189–4198, 2009.

[13] J. Zhu, S. Wei, D. Rutman, N. Haldolaarachchige, D. P. Young,and Z. Guo, “Magnetic polyacrylonitrile-Fe FeO nanocom-posite fibers-electrospinning, stabilization and carbonization,”Polymer, vol. 52, no. 13, pp. 2947–2955, 2011.

[14] L. Bokobza, “Multiwall carbon nanotubes-filled natural rubber:electrical and Mechanical properties,” Express Polymer Letters,vol. 6, no. 3, pp. 213–223, 2012.

[15] W. S. Khan, R. Asmatulu, and M. B. Yildirim, “Acoustical prop-erties of electrospun fibers for aircraft interior noise reduction,”Journal of Aerospace Engineering, vol. 25, no. 3, pp. 376–382,2012.

[16] A. Szentes, C. S. Varga, G. Horvath et al., “Electrical resistivityand thermal properties of compatibilized multi-walled crabonnanotube/Polypropylene composites,” EXpress Polymer Letters,vol. 6, no. 6, pp. 494–502, 2012.

[17] J. Zhu, S. Wei, J. Ryu, and Z. Guo, “Strain sensing elas-tomer/carbon nanofibers ‘Metacomposites’,” Journal of PhysicalChemistry C, vol. 115, no. 27, pp. 13215–13222, 2011.

[18] N. F. Mott and E. A. Davis, Electronic Process on Non-CrystallineMateials, Oxford University Press, New York, NY, USA, 2ndedition, 1979.

[19] L. Wang, L. Zhang, and M. Tian, “Improved polyvinylpyrroli-done (PVP)/graphite nanocomposites by solution compound-ing and spray drying,” Polymers for Advanced Technologies, vol.23, no. 3, pp. 652–659, 2012.

[20] F. H. Gojny, M. H. G. Wichmann, B. Fiedler et al., “Evaluationand identification of electrical and thermal conduction mecha-nisms in carbon nanotube/epoxy composites,” Polymer, vol. 47,no. 6, pp. 2036–2045, 2006.

[21] B. Sundaray, V. J. Babu, V. Subramanian, and S. T. Natara-jan, “Preparation and characterization of electrospun fibersof Poly(Methyl Methacrylate) single walled carbon notubecomposites,” Journal of Engineered Fibers and Fabrics, vol. 3, no.4, pp. 39–45, 2008.

[22] L. Bokobza, “Multiwall carbon nanotube-filled natural rubber:electrical and Mechanical Properties,” Express Polymer Letters,vol. 6, no. 3, pp. 213–223, 2012.

[23] N. Norkhairunnisa, A. Azizan, M. Mariatti, H. Ismail, and L. C.Sim, “Thermal stability and electrical behavior of polydimethyl-siloxane nanocomposites with carbon nanotubes and carbonblack fillers,” Journal of Composite Materials, vol. 46, no. 8, pp.903–910, 2011.

[24] B. Qiao, X. Ding, X. Hou, and S. Wu, “Study on the electrospunCNTs/polyacrylonitrile based nanofiber composites,” Journal ofNanomaterials, vol. 2011, Article ID 839462, 7 pages, 2011.


[25] P.Gupta, R.Asmatulu, R. Claus, andG.Wilkes, “Superparamag-netic flexible substrates based on submicron electrospun Estanefibers containingMnZnFe-Ni nanoparticles,” Journal of AppliedPolymer Science, vol. 100, no. 6, pp. 4935–4942, 2006.

[26] W. S. Khan, R. Asmatulu, Y. H. Lin, Y. Y. Chen, and J.Ho, “Electrospun polyvinylpyrrolidone-based nanocompositefibers containing (Ni

0.6Zn0.4)Fe2O4,” Journal of Nanotechnol-

ogy, vol. 2012, Article ID 138438, 5 pages, 2012.[27] R. Asmatulu, B. Zhang, and N. Nuraje, “A ferrofluid guided

system for the rapid separation of the non-magnetic particlesin a microfluidic device,” Journal of Nanoscience and Nanotech-nology, vol. 10, no. 10, pp. 6383–6387, 2010.

[28] M. Naebe, T. Lin, M. P. Staiger, L. Dai, and X. Wang,“Electrospun single-walled carbon nanotube/polyvinyl alcoholcomposite nanofibers: structure-property relationships,” Nan-otechnology, vol. 19, no. 30, Article ID 305702, 2008.

[29] W. Edward and W. D,Morphological and mechanical propertiesof carbon nanotubes/polymer composites via melt compounding[M.S. thesis], North Carolina State University, Raleigh, NC,USA, 2005.

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