Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties

Accepted Manuscript Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties Pallavi Gupta, Mohit Rajput, Nikhil Singla, Vijayesh Kumar, Debrupa Lahiri PII:

S0032-3861(16)30105-7

DOI:

10.1016/j.polymer.2016.02.025

Reference:

JPOL 18457

To appear in:

Polymer

Received Date: 4 December 2015 Revised Date:

11 February 2016

Accepted Date: 12 February 2016

Please cite this article as: Gupta P, Rajput M, Singla N, Kumar V, Lahiri D, Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties, Polymer (2016), doi: 10.1016/j.polymer.2016.02.025. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Graphical abstract

ACCEPTED MANUSCRIPT Manuscript

Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties

1

RI PT

Pallavi Gupta1,2, Mohit Rajput2, Nikhil Singla2, Vijayesh Kumar1,2, Debrupa Lahiri1,2* Centre of Nanotechnology, 2Biomaterials and Multiscale Mechanics Lab, Department of Metallurgical

M AN U

*Corresponding author. Tel.: +91-1332-28-5137.

SC

and Materials Engineering, Indian Institute of Technology Roorkee, Uttarakhand 247667 (INDIA)

E-mail address: [email protected] (Debrupa Lahiri) Highlights

Abstract

TE D


Alternating voltage and current assisted CNT alignment in polymer matrix was achieved
Mechanical and electrical properties of polymer were anisotropically enhanced with alignment
Current assisted alignment showed higher anisotropic conductivity as compared to voltage

EP

Polymer matrix composites, reinforced with aligned carbon nanotubes (CNT), have a great

AC C

potential in myriads of applications including flexible electronic and biomedical devices. However, effectively aligning the CNTs inside any matrix has always been a challenge. Present study deals with fabrication of an aligned carbon nanotube reinforced polymer matrix composite and effect of the methods of alignment on anisotropic properties of the composite. Multi-walled carbon nanotubes (MWCNT) reinforced Polyvinylidene fluoride (PVDF) composite with uniform dispersion and alignment of CNTs is fabricated by solution casting technique. CNTs are aligned with the application of alternating voltage as well as pulsed current. The voltage-assisted films have shown good dispersion and alignment of CNTs

1

ACCEPTED MANUSCRIPT inside PVDF matrix. On the other hand, the current-assisted alignment led to the formation of shortest, continuous path for the flow of electrons and hence, resulted in formation of highly anisotropic conductive film. Directly current passage assisted alignment of CNTs in the composite film records an impressive 360% improvement in conductivity in the direction

RI PT

parallel to the alignment as compared to the structure with randomly aligned CNT. At the same time, the composite in transverse direction to the alignment was totally insulating, indicating the efficiency of alignment. With the addition of only 0.5 wt% CNTs to PVDF

SC

matrix, film shows improvement of elastic modulus and tensile strength by 180% and 150%, respectively, as compared to pure PVDF film. However, the films behaved mostly isotropic

M AN U

in terms of mechanical properties, showing improvement in all the directions with CNT reinforcement. This study provides effective way to align CNT in thermoplastic matrix to tailor the directional electrical conductivity significantly.

TE D

Introduction

Owing to high tensile strength and extraordinary electron mobility, carbon nanotubes (CNTs) are ideal candidate as filler material for improving the mechanical and electrical properties of

EP

polymer matrix composites[1]. CNT reinforced polymer composites are favorite candidates for electrically conductive adhesives, as the reinforcement phase strongly enhances the

AC C

electrical properties of a polymer material when a percolated net-work of interconnected nanotubes is formed. Hybrid CNT devices, such as, broad- band photodetectors[2], hybrid and all-carbon solar cells[3][4], electrically conductive photonic crystals[5] and photothermal nanotube - polymer composites[6] for biomedical applications[7] have also been researched so far. In most of these applications, charge transfer and hence performance can be increased by forming a continuous (percolated) network of interconnected nanotubes inside a polymer matrix.

2

ACCEPTED MANUSCRIPT Electrical properties of 1-D conductor CNTs are strongly dependant on their structure. Under the ballistic conduction phenomenon, electrical resistivity of MWCNTs is 3X10-5 Ω cm[8][9]. This indicates that CNTs show 1000 times better conductivity than metals, such as, copper at room temperature. But, due to 1-D nanostructure, electrons prefer moving along the

RI PT

tubes’ axis. As a result, CNT shows significant difference in conductivities along axial and radial direction with the values being 1000 S/m and 150 S/m, respectively[10]. To take advantage of the anisotropic conductivity of CNTs in composite structure, there is a need to

SC

have all the CNTs in a similar orientation within polymer matrix. Such aligned CNT polymer composites are expected to show very high conductivity only in alignment direction, as

M AN U

compared to other directions. Such anisotropic conductivity has applications in field-effect transistors, film based flexible device fabrication and interconnects for electronic devices[11][12]. In biomedical fields, these materials are preferred as scaffolds for generating electric field using low potentials to induce cell polarization. Shin et al. have engineered

TE D

muscle-based biohybrid actuators with aligned CNT forest microelectrode arrays and incorporated them into scaffolds for cell stimulation[13]. These specific examples have generated significant interest in the field of biorobotics, as much controlled movement over

EP

their actuation behavior can be achieved. Present authors have used such composites with

AC C

anisotropic electrical conductivity to align neuronal cells in scaffolds for neural tissue engineering in another study[14]. Another attribute of CNT reinforcement to polymer is on the mechanical properties of the composite. Polymer fiber easily breaks under tensile forces mostly due to the sliding action of neighboring polymeric chains, which are bonded together by the weak van der Waals force. CNTs, as reinforcement to polymer matrix, can hold the polymer chains together to decrease their slippage and improve the mechanical strength of the polymer[15]. CNTs have very high Young’s modulus of ~1 TPa and tensile strength in the range of 11–63 GPa, which makes 3

ACCEPTED MANUSCRIPT them promising as ultra-high-strength reinforcements in high-performance polymer matrix composites[16]. Hence, CNT alignment inside polymer matrix can be used as a tool to tailor the electrical

RI PT

properties along with mechanical properties. The mechanical and electrical properties of the final composite depend upon the degree of CNT alignment, especially when the composite is evaluated for their performance in parallel or transverse direction to the CNT orientation. Till today, various techniques have been used for aligning CNTs in matrix, such as, mechanical

SC

force[17][18][19][20][21], magnetic field[22][23][24][25][26][27], electric field[14][28][29]

M AN U

[30][31][32][33][34][35][36][37][38][39], shear flows[40] and electrospinning[41][42]. The use of mechanical force for CNT alignment requires uniaxial stretching of multi-walled CNT (MWCNT)/polymer films at higher temperature[17], extrusion of the melted composite through a rectangular shaped die and finally drawing the film before cooling[18] in laser ablation reactor[19]. It is also reported to be achieved by employing a melt processing

TE D

technique[20], where aligned polymethyl methacrylate (PMMA)/single-walled CNT (SWCNT) composite films and fibers were fabricated along the flow direction. Another

EP

method is also used for fabricating thin electrically conductive composite films by sliding a thin film of random SWCNT/polymer ink between two flat glass substrates under

AC C

pressure[21]. Magnetic field assisted alignment of CNT in polymer matrix is also possible by applying field during high pressure filtration of CNT suspension[22][23][24]. Electric fields have been exploited to align CNTs in different possible ways. Highly-oriented CNTs were prepared in different solvents using an AC electric field[31][32][33]. The electric fieldguided assembly of CNTs has attracted much attention due to its potential in scaling up. Anisotropic structure of CNT and its electrical properties render a rapid response to applied electric fields, resulting in CNT orientation along the field direction[43][44][45]. Although both direct current (DC) [34][46] and alternating current (AC) [45][34][47] electric fields are 4

ACCEPTED MANUSCRIPT used to induce CNT alignment, AC fields are proven to be more efficient for this purpose. DC field make the particles charged (functionalized CNTs) move in the direction parallel to the surface. Therefore, clustering of CNTs occurs at the electrode, carrying the charge opposite to the charge on the surface of the nanotubes. In contrast, application of AC electric

RI PT

field results in an aligned CNT network formed between the electrodes, governed by dielectrophoresis and orientation phenomena (owing to the anisotropic electrical conductivity of CNTs)[48]. It is likely to result in alignment of CNTs in matrix with their longitudinal axis

SC

parallel to applied electric field. Similar results have been shown with the application of alternating electric field in the SWCNT-UH (urethane dimethacrylate (UDMA) and 1,6-

M AN U

hexanediol dimethacrylate blend) system, where a relatively continuing networks was formed as compared to the direct electric field[49]. Martin et al. dispersed CVD-grown multi-wall carbon nanotubes in epoxy matrix based on a bisphenol-A resin and amine hardener. Both AC and DC electric fields were applied during nanocomposite curing to induce the formation

TE D

of aligned conductive nanotube networks between the electrodes. It was observed that the CNT network structure formed was more uniform and aligned in AC fields in comparison to

EP

DC field[34].

Due to the alignment of CNTs in matrix, electrical and mechanical properties of the

AC C

composite also become superior and anisotropic. Prassse et al. presented initial results on electrical anisotropy in epoxy matrix due to electric field induced alignment of carbon nanofibres for field emission applications. The fibre content of 1 wt% and above have shown maximal anisotropy of the resistance of about 1 order of magnitude[50]. Park et al. proved that the conductivity and dielectric properties of aligned urethane dimethacrylate and 1,6hexanediol dimethacrylate (9:1 blend) -CNT composites can be tuned over a broad range by proper control of the applied field strength, frequency, and time[49]. Another study reported 46% decrease in resistivity for 0.01 wt.% non-aligned nanotubes. Resistivity of aligned 5

ACCEPTED MANUSCRIPT nanotubes at 200 V was found to be reduced by one order of magnitude at 19 V from neat epoxy[51]. Wang et al. reported improvement in tensile strength from 8 MPa to 21.1 MPa and Young’s modulus from 415 MPa to 843 MPa in the CNT orientation direction of 3 wt.%

RI PT

CNT reinforced epoxy composite[52]. A number of studies have used electrical field (voltage) as the tool for aligning the CNTs inside polymer matrix. However, none have tried passing current directly through the polymer matrix, before curing, to align the CNTs in the final product as free-standing

SC

polymer composite film. Current always prefers a shortest and less resistant path to flow.

M AN U

Thus, direct passage of current might have the potential to align the CNTs in a linear pattern across the composite to create its shortest path of flow. This would have not only aligned the CNTs, but would make an end to end contact of CNTs and increase the conductivity of the composite significantly. Further, better alignment would also make the composites highly anisotropic, i.e., almost no conductivity in directions other than alignment direction.

TE D

However, as per the authors’ knowledge, no reports are available in open literature exploring the effect of passage of current directly through matrix on aligning the CNTs inside polymer

EP

matrix in the cured composite. Thus, this can be considered as a very unique idea, which can lead to a significant improvement in the effort of aligning CNTs in polymer matrix

AC C

composites and thus making them highly conducting. In light of the current scenario, the present study explores the possibility of fabricating PVDF composite, reinforced with aligned CNTs. The alignment of CNTs inside PVDF matrix is tried under the influence of AC electric field as well as direct passage of alternating current. The current is applied to form end-to-end alignment of the CNTs inside PVDF matrix. The CNTs are assumed to form a linear path of minimal distance between the electrodes for direct passage of current. Along with fabrication of anisotropic film, the effect of CNT alignment on electrical and mechanical properties in both parallel and transverse direction of alignment 6

ACCEPTED MANUSCRIPT is also evaluated. This study focuses on fabrication of anisotropically conducting films for the application in modern electronic as well as biomedical devices. Methods and materials

RI PT

Solution preparation PVDF powder (average Mw. 534000, density: 1.74 g/cc) was procured from Sigma Aldrich, India. MWCNT used were with outer diameter of 10-12 nm, length of 8-12 µm, density of 1.8 g/cm3 and 95% purity, procured from CNano Technology Limited, Beijing, China. CNTs

SC

were dispersed in 50 ml DMF using probe sonication for 2 hours. In another solution, PVDF

M AN U

was mixed with 75 ml DMF at 60˚C on hot plate with magnetic stirring for 2 hours at 300 rpm. In the next step, CNT dispersed solution was added drop wise to PVDF solution, which was simultaneously stirred with the help of magnetic stirring for 2 hours at 70°C and 400. Finally, the mixed solution was further ultrasonicated for 2 more hours (at 500 kJ energy and 5 seconds ON and 3 seconds OFF cycle) to form a well dispersed solution. The solutions

TE D

were prepared in such a way to have 0.5 wt.% CNT in the final composite structure. Prior to solution preparation, functionalization of CNT was performed through refluxing

EP

process in concentrated acetic acid for 3 hr. The functionalization process was followed by washing the CNT through centrifuge. The washed CNT were dried inside oven to obtain in

AC C

the powdered form.

Alignment of CNT in PVDF matrix An amount of 125 ml PVDF solution was equally distributed into 5 glass molds. Three of those molds were placed in hot air oven at 50 °C and the temperature was continuously increased at the rate of 5°C per hour to a maximum of 90˚C till the dried composite films were obtained. Out of these three, one each were exposed to an alternating bias of 220V and 500V respectively, while the third one was kept without the influence of any electric field, 7

ACCEPTED MANUSCRIPT while curing. Alternating pulsed currents, from 220V and 500V source, were directly applied separately on remaining 2 glass molds containing PVDF-CNT solution at room temperature as almost dried films were achieved after current application. For applying the currents to both the solutions, electrodes were put inside PVDF-CNT solution on the ends of molds. On

RI PT

the other hand, to apply alternating voltage, the electrodes were attached to the outer side of the molds. Fracture surface characterization of films

SC

The morphological characterization of PVDF film, random PVDF-CNT composite film and aligned PVDF-CNT composite film was performed using scanning electron microscopy

Evaluation of mechanical behavior

M AN U

(SEM, EVO 18 special edition, Ziess, Germany).

Tensile properties of composite films were measured at room temperature using a universal

TE D

test device (Bose Electro Force® 3200 series III test instrument) from Bose CorporationElectroForce Systems Group, USA. Samples were prepared and tested according to ASTM D638, at a grip separation rate of 0.1mm/s. Sample dimension were 30 mm x 6.5 mm with

EP

gauge length of 9 mm. The sample thickness varied between 0.01 mm to 0.03 mm. Tests were performed in triplicates for each type of films at a grip separation rate of 0.1 mm/s to

AC C

analyze Young’s modulus and ultimate tensile strength (UTS). Evaluation of electrical properties The electrical conductivity of the films was measured at room temperature using Keithley 4probe system that includes Model 6220 DC current Source (measurement range : 100 mA 0.1 pA) and Model 2182 nanovoltmeter (measurement range: 120 V to 1 nV) from Keithley Instruments, Inc., USA.

8

ACCEPTED MANUSCRIPT The volume resistivity (ρ) was then calculated from the characteristic I−V curves by taking into account the geometrical characteristics of the sample, using the following relationship: ρ = V× A / I x L

RI PT

Where V is the applied voltage, I is the measured current, A is the area of the electrodes, and L is the distance between electrodes, corresponding to the thickness of the sample.

Results and discussion Aligned CNT network formation

M AN U

σ =1/ ρ

SC

Electrical conductivity (σ) was then calculated as the inverse of the resistivity (ρ):

Composite films were casted using solution mixing technique. DMF is used as liquid medium

TE D

for the assisting of dispersion of CNTs in polymers. The melting point of PVDF (177˚C) is higher than the boiling point of DMF (153˚C). This helps in removal of solvent by evaporation during and after curing of the polymer, without damaging the composite

EP

structure.

Agglomeration of CNT was found to be the main drawback during the casting of composite High surface energy of CNT, as well as, significant difference in thermal

AC C

films.

conductivities of PVDF (0.241W/m-K)[53] and CNT (6600W/m-K)[54] led to the enhanced CNT agglomeration. Due to high thermal conductivity and specific heat, CNT rich regions heat up more as compared to insulating PVDF. This temperature difference between PVDF and CNT increases energy of reinforcement phase and CNT rich regions try to become stabilize by decreasing its surface area. This phenomenon leads to formation of clusters of CNT in the PVDF matrix. In order to achieve homogenous composition throughout the composite film, the temperature was increased slowly, so as to maintain the minimum 9

ACCEPTED MANUSCRIPT possible temperature difference between CNT and PVDF. Thus, in this study, the curing of the composite film was optimized by decreasing the temperature at a rate of 5˚C / h to avoid

TE D

M AN U

SC

RI PT

segregation of CNTs in PVDF matrix.

Figure. 1 Digital images of (a) PVDF; (b) random; (c) voltage assisted aligned CNT- PVDF composite; (d) and directly current passage assisted aligned CNT- PVDF composite.

EP

In case of directly current passage assisted CNT alignment, the energy of the composite increased instantaneously due to very high rate of alignment and electrical conductivity.

AC C

Electrical sparking was also observed in the composite cured at a voltage difference of 500 V and as a result the polymer matrix melted at places and film structure got distorted. The morphologies and distribution of CNT in different PVDF-CNT composites are presented in digital images of the films in figure 1. Corresponding schematic and the SEM images of the films are also shown in figure 2. Figure 2e shows the fracture surface of PVDF film without any CNT reinforcement. The composite fabricated with electric field of 220 V is not being reported here as they did not show any difference in conductivity as compared to

10

ACCEPTED MANUSCRIPT composites without application of any field. Thus, it is assumed application of only 220V bias is not enough to align CNTs in PVDF matrix. The digital images in figures 1 b and c present identical black color film, which indicates uniform distribution of CNT inside polymer matrix in random and field aligned composite structures. In the SEM micrographs

RI PT

also, CNTs are found distributed uniformly in the PVDF matrix (figure 2f and 2g). However, the alignment of CNTs is random in the composite without any field (figure 2f), whereas they show a definitive alignment in the other one in the direction of the applied filed, as marked by

SC

arrows in figure 2g. On the contrary, the composite fabricated with current (figure 1d) shows macro-scale segregation of CNTs along channel in the polymer matrix, as indicated by the

M AN U

back colored region, with rest of the polymer being deficient in filler. These channels are found to be extended in a way to connect the electrodes in the bulk structure. CNT aligned network is also found to be most prominent in the SEM images of the composite fabricated with application of current (figure 2h). This structures show two distinct

TE D

regions at higher magnification also, as presented in figures 2h and i. Figure 2i corresponds to CNT deficient light shaded region at macro scale (figure 1d), which resembles the structure

EP

of only PVDF in figure 2e. On the contrary, the CNT rich black channel like regions reveals a continuous aligned dense network of tubular structure (figure 2h). The diameter of such tubes

AC C

are in the range of CNTs and they are absent in the CNT deficient region (figure 2i). Thus, these tubular structures are logically assigned to be the aligned CNTs, which might have been covered with thin layer of polymer. This observation indicates segregation of CNTs in PVDF matrix and formation of a conducting path across electrode by end to end contact of CNTs. The SEM image, captured in the linear CNT alignment region (Figure 2h), further corroborates this observation. It reveals perfect alignment of bunch of CNTs in a singular direction (figure 2h and inset). This happens to be the direction of the applied field and current. 11

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure. 2 Schematics and SEM images of PVDF(a,e), random(b,f), voltage assisted aligned CNT- PVDF composite (c,g) and directly current passage assisted aligned CNT- PVDF composite(d,h,i) respectively. Image h and i correspond to the CNT rich and CNT deficient regions in the directly current passage assisted aligned CNT- PVDF composite film respectively.

12

ACCEPTED MANUSCRIPT The nanotubes experience polarization under the influence of electric field. This polarisation has contributing components in both, parallel and the radial direction of the axes of nanotube. The magnitude of both the parallel and radial component is decided by polarisability tensor of the nanotube. The parallel direction of the tube axis has greater polarisability as compared to

RI PT

radial axis under the influence of electric fields[55][56]. This differential polarizability of nanotubes develops a torque, responsible for alignment of CNTs in the direction of the applied electric field against the viscous drag of the matrix. The degree of CNT dispersion

SC

and alignment is governed by the amount of applied electric field per unit length[57]. In the present study, AC electric field is chosen over DC, based on the knowledge gathered by other

M AN U

research groups, as discussed in the introduction section.

A markedly different behavior is observed when alternating pulsed current is applied to the PVDF-CNT film as shown in figure 1d and figure 2d, 2h. The macroscopic channel-like

TE D

black structures are formed inside PVDF matrix after application of current (figure 1d). The formation of such an aligned network was faster when the magnitude of the applied current was increased. Current between electrodes, separated via 500V, led to an almost

EP

instantaneous CNT alignment between the electrodes. The microstructure of the PVDF-CNT composite, fabricated by direct passage of current between electrodes separated via 220V

AC C

voltage, is shown in figure 2h. Electric conductivity of the CNTs (∼103 S m−1)[58] is much higher as compared to that of the PVDF (5X10-11 S m−1). This difference in conductivity dictates the changes in the CNT network in such composite structure. The CNTs are assumed to be forming a linear path of minimal distance between the electrodes to help in assisting current directly pass through. It can be concluded from the microstructural analysis of these PVDF-CNT composites that the electric field strength in case of voltage assisted alignment led to the alignment of CNT inside PVDF matrix, while current assistance aligned the CNT by joining them end-to-end. 13

ACCEPTED MANUSCRIPT Electrical properties CNT reinforcement can effectively enhance the conductivity of the polymer[59][57][60][61]. CNTs are also good candidate for providing anisotropic electrical conductivity in polymer

RI PT

matrix, if aligned. Researchers have tried different methods to align the CNTs in viscous polymer matrix[62][20][63][27][23][64][18]. However, electric field alignment is reported to be the most effective method for this purpose[48].

SC

Figure 3 shows the resulting conductivities of the cured composites as a result of CNT reinforcement in the directions parallel and perpendicular to the field as well as current.

M AN U

Results indicate that incorporation of CNTs inside PVDF matrix caused increase in conductivity by the order of 10, i.e., 103 S-cm, as compared to only PVDF film with electrical conductivity of 10-7 S-cm). Application of electric field records 28% increase in conductivity in parallel direction of alignment as compare to random film, while the transverse direction

AC C

EP

TE D

shown 58% decrease in electrical conductivity.

14

ACCEPTED MANUSCRIPT

0.009 0.008

RI PT

0.006 0.005 0.004 0.003

SC

Conductivity (S-cm)

0.007

0.002

M AN U

0.001 0.000

PVDF random V parallel endicular t(parellel)endicular)t (parellel)endicular) 500 0V perp curren nt(perp curren t (perp 50 220V 0V curre 500V 0V curren 22 50

TE D

Figure. 3 Comparison between conductivities of all the films

The composite film, synthesized under application of alternating pulsed current, has shown highly anisotropic characteristics with very high aligned network of CNTs. At current applied

EP

with 220V bias, 360% increase in conductivity was observed in parallel direction, as compared to random one. On the other hand, the transverse direction has shown very low

AC C

conductivity. While current with 500V bias led to the 60% increase in the conductivity, which is much lower than what is achieved with current applied at a voltage difference of 220 V. This is attributed to the partial melting and distortion of film due to high passage of current at 500V during fabrication process, which might have caused extraordinary increase in temperature at places. Reports are available on exploring the effect of electrical conductivity on aligning the CNTs in different polymer matrices[48][49][57][60][62][10][65]. Larijani et al. has shown effect of magnetic, a.c. and d.c. electric field on CNT alignment inside polycarbonate matrix. 15

ACCEPTED MANUSCRIPT Application of a.c. electric field and magnetic field in the system led to the formation of relatively aligned networks while d.c. electric field was found not so effective in aligning CNTs[59]. However, in these studies, the CNT are not connected end-to-end with each other in alignment direction. Hence, electrons do not get a continuous path to travel faster and more

RI PT

efficiently from one end to another in a device. So, the present study aims to fabricate highly anisotropic alignment of CNT in PVDF matrix, so that the electrons get the shortest and continuous path to travel in a device from one end to another without any hindrances and

SC

deflections.

It has been demonstrated in the present study that alignment via alternating field is an

M AN U

effective method for the alignment of CNT in one direction. However, it forms discontinuous reinforcement as the CNT will become nearly parallel but not joined by end to end with each other (Figure 2c). On the other hand, CNT alignment with passage of current results in continuous channels of reinforcement within the polymer matrix, where CNTs are joined end

TE D

to end with each other and form an uninterrupted path (Figure 2d). Due to the formation of continuous channels, electrons get direct path of flow and results in drastic increase in conductivity. Till date, no report is available in open literature on aligning the CNTs in

EP

composite by application of current, which has a potential to make continuous CNT nano-

AC C

fiber channels inside the matrix. Thus, this is a unique idea, which can give a very significant improvement in the effort of aligning CNTs in polymer matrix composites. However, due to strong alignment, the CNTs inside polymer matrix is found to form macroscopic CNT rich channel like structure, whereas the remaining part of matrix remains deficient in CNT (Figure 1d). Thus, other attributes of the composite films, like mechanical properties might be nonuniform. This aspect needs more research to explore if further improvement towards uniformity in structure can be achieved during alignment of CNTs in polymer matrix applying current.

16

ACCEPTED MANUSCRIPT

Mechanical Properties Mechanical behavior of polymer-CNT composites are generally function of various

RI PT

parameters, like, CNT content, aspect ratio, dispersion, alignment, interfacial interaction, morphology and technique of preparation of the composite structure.

Mechanical properties are dependent on load transfer between CNTs and matrix and better load transfer means enhanced mechanical properties. This can be achieved by having

SC

effective dispersion of CNT inside polymer matrix and better interfacial bonding between

M AN U

matrix and reinforcement phase. Functionalization of nanotubes often helps in achieving both of these. Liu et al. reported increase in tensile strength and modulus with the increase of CNTs content in polymer composite[66]. Qian et al. observed 35% and 42% increase in modulus for a composites filled with 1 wt. % short and long tubes, respectively. A 25% improvement in failure stress is noted for both types of CNTs[67]. As stated in previous

TE D

studies, composites reinforced with functionalized nanotubes are expected to have large interfacial shear strengths, due to better dispersion as well as bonding developed between

AC C

EP

reinforcement and matrix material[68].

17

ACCEPTED MANUSCRIPT

(a)

RI PT

1000

SC

500

M AN U

Young'sModulus (MPa)

1500

0 PVDF

Random

50

TE D

(b)

EP

20

AC C

Ultimate Tensile strength (MPa)

40

30

500V (parallel) 500V (perpendicular)

10

0 PVDF

Random

500V (parallel) 500V (perpendicular)

Figure. 4 Comparison between Young’s modulus (a) and UTS (b) of all the films

18

ACCEPTED MANUSCRIPT The aim of this study is to find out the effect of alignment of CNT on mechanical properties of polymer matrix. For better understanding of the property variation caused by alignment, other factors, as discussed above, were kept as similar as possible. The analysis was done on the composite films, fabricated using alternating voltage, as it yields uniform and

RI PT

homogenous films. The composites prepared applying current were not evaluated for mechanical properties, due to their macroscopic inhomogeneity in CNT distribution, as discussed before.

SC

It is observed that the addition of 0.5 wt% CNTs to PVDF, even without any alignment, results in improvement of elastic modulus and ultimate tensile strength (UTS) by 180% and

M AN U

150%, respectively, as compared to pure PVDF film. The aligned composite film, fabricated by applying alternating voltage of 500 V, shows 26% and 30% improvement in elastic modulus and UTS, respectively, in the alignment direction. Further, the transverse direction recorded an improvement in elastic modulus and UTS by 28% and 46%, respectively with

TE D

respect to random film. Though, with large error bars in the elastic modulus data, this improvement cannot be accepted as significant. Thus, mechanical properties do not show much anisotropy in aligned and transverse direction, which is not in line with the electrical

EP

conductivity of these films.

AC C

However, such mechanical behavior in aligned PVDF-CNT structures can be explained in terms of the structure of PVDF and strengthening mechanism offered by CNT.

The

thermoplastic polymers have unique tendency to align their molecular chains along the pull direction during tensile loading[69]. Therefore, during evaluation of the tensile properties of the films along the direction of alignment, CNT and PVDF polymeric chains align themselves in same direction. As the pull force is applied, strong interfacial bonding between functionalized CNT and the PVDF matrix allows effective load transfer from PVDF chains to CNT, across a large interfacial area. Deformation in CNT is negligible in comparison with

19

ACCEPTED MANUSCRIPT PVDF, because of very high strength of CNT. Thus, it maintains the integrity of PVDF-CNT films under tensile loading. In case of the tensile tests performed in transverse direction, the orientation of CNT is perpendicular to that of stretched PVDF chains. The pattern of orientation of PVDF chains and CNT, in this case, provides bridging effect in perpendicular

RI PT

direction of load application. This bridging by CNT hinders the relative slipping of polymeric chains against each other and the structure withstands higher stress without causing much deformation. Therefore, almost similar elastic modulus is observed in the transverse direction

SC

of the aligned film. However, hindrance in slipping of polymeric chains through CNT bridging has more impact on plastic deformation and thus improvement in UTS is higher in

M AN U

perpendicular/transverse direction, than in alignment direction.

The random film has CNT oriented in all directions. Thus, the number of effective load bearing CNT in any direction of random film is lower than that in aligned direction and higher than in transverse direction of the aligned film. The opposite is true for the CNTs

TE D

available for bridging the relative slipping of polymeric chains. Thus, the strength of random film is lower than that of aligned composite structure in any direction.

EP

Though the main aim of this study is to fabricate an anisotropically conductive film for electronic applications, but the electronic devices may easily get damaged due to its very thin

AC C

construct. Hence, the increase in mechanical properties of aniostropically conductive membrane offers an additional advantage to the fabricated devices.

Conclusion

In the present study, macro-scale CNT reinforced PVDF films are fabricated in a very simple and reproducible method. Alignment of CNT inside PVDF matrix is achieved by applying external alternating voltage as well as alternating pulsed current during fabrication process. Field alignment method is an effective method to yield aligned nanotubes in matrix of 20

ACCEPTED MANUSCRIPT material but lags in the formation of end to end joined channels of nanotubes. The probability of formation of shortest path for the flow of electrons increases by the use of alternating pulsed current on PVDF-CNT composite. The field assisted PVDF-aligned CNT films have shown 28% increase in conductivity in parallel direction of alignment, while transverse

RI PT

direction have shown 58% decrease in electrical conductivity, as compared to its random counterpart. Alternating pulsed current passage assisted PVDF-aligned CNT film shows an impressive 360% increase in conductivity in parallel direction (over random sample). The

SC

transverse direction becomes almost insulating. Addition of 0.5 wt% CNTs to PVDF matrix results in 180% and 150% improvement in elastic modulus and UTS, , respectively, as

M AN U

compared to pure PVDF film. This highly anisitropic, uniaxially conductive PVDF- aligned CNT composite can be excellent candidates for fabrication of flexible nanoelectronics as well as biomedical devices.

TE D

ACKNOWLEDGMENTS

DL acknowledges Dr. Arvind Agarwal, Professor, Florida International University, USA and

EP

CNano, Beijing, China for generously providing the CNT for this research work. DL also acknowledges the financial support from the faculty initiation grant (FIG-100613) by IIT

AC C

Roorkee for carrying out this research. The authors also wish to thank the laboratory staffs from the Centre for Nanotechnology and the Department of Metallurgical and Materials Engineering, IIT Roorkee, for maintaining the experimental facilities.

References [1]

J.Z. Kovacs, B.S. Velagala, K. Schulte, W. Bauhofer, Composites Science and

Technology, Two percolation thresholds in carbon nanotube epoxy composites, Compos. Sci. Technol. (2006) 1–12. doi:10.1016/j.compscitech.2006.02.037. 21

ACCEPTED MANUSCRIPT [2]

M.S. Arnold, J.D. Zimmerman, C.K. Renshaw, X. Xu, R.R. Lunt, C.M. Austin, et al.,

Broad spectral response using carbon nanotube/organic semiconductor/C60 photodetectors., Nano Lett. 9 (2009) 3354–3358. doi:10.1021/nl901637u. [3]

X. Li, Y. Jung, K. Sakimoto, T.-H. Goh, M. a. Reed, A.D. Taylor, Improved

Energy Environ. Sci. 6 (2013) 879. doi:10.1039/c2ee23716d. [4]

RI PT

efficiency of smooth and aligned single walled carbon nanotube/silicon hybrid solar cells,

A.S. Cells, M.P. Ramuz, M. Vosgueritchian, P. Wei, C. Wang, Y. Gao, et al.,

Evaluation of Solution-Processable Carbon-Based Electrodes for, (2012) 10384–10395.

Y. Imai, C.E. Finlayson, P. Goldberg-Oppenheimer, Q. Zhao, P. Spahn, D.R.E.

SC

[5]

Snoswell, et al., Electrically conductive polymeric photonic crystals, Soft Matter. 8 (2012)

[6]

P.

Xu,

J.

Loomis,

B.

M AN U

6280. doi:10.1039/c2sm06740d. Panchapakesan,

Photo-thermal

polymerization

of

nanotube/polymer composites: Effects of load transfer and mechanical strength, Appl. Phys. Lett. 100 (2012). doi:10.1063/1.3698343. [7]

S. Ramakrishna, J. Mayer, E. Wintermantel, K.W. Leong, Biomedical applications of

TE D

polymer-composite materials: A review, Compos. Sci. Technol. 61 (2001) 1189–1224. doi:10.1016/S0266-3538(00)00241-4. [8]

a. Bachtold, M. Henny, C. Terrier, C. Strunk, C. Schönenberger, J.P. Salvetat, et al.,

EP

Contacting carbon nanotubes selectively with low-ohmic contacts for four-probe electric measurements, Appl. Phys. Lett. 73 (1998) 274–276. doi:10.1063/1.121778. C. Berger, Y. Yi, Z.L. Wang, W. a. De Heer, Multiwalled carbon nanotubes are

AC C

[9]

ballistic conductors at room temperature, Appl. Phys. A Mater. Sci. Process. 74 (2002) 363– 365. doi:10.1007/s003390201279. [10]

W.A. Deheer, W.S. Bacsa, A. Châtelain, T. Gerfin, R. Humphrey-Baker, L. Forro, et

al., Aligned carbon nanotube films: production and optical and electronic properties., Science. 268 (1995) 845–847. doi:10.1126/science.268.5212.845. [11]

S. Park, M. Vosguerichian, Z. Bao, A review of fabrication and applications of carbon

nanotube

film-based

flexible

electronics.,

Nanoscale.

5

(2013)

1727–52.

doi:10.1039/c3nr33560g. 22

ACCEPTED MANUSCRIPT [12]

S. Chae, Y. Lee, Carbon nanotubes and graphene towards soft electronics, Nano

Converg. 1 (2014) 15. doi:10.1186/s40580-014-0015-5. [13]

S.R. Shin, C. Shin, A. Memic, S. Shadmehr, M. Miscuglio, H.Y. Jung, et al., Aligned

Carbon Nanotube-Based Flexible Gel Substrates for Engineering Biohybrid Tissue Actuators,

[14]

RI PT

Adv. Funct. Mater. 25 (2015) 4486–4495. doi:10.1002/adfm.201501379. P. Gupta, S. Sharan, P. Roy, D. Lahiri, Aligned carbon nanotube reinforced polymeric

scaffolds with electrical cues for neural tissue regeneration, Carbon N. Y. 95 (2015) 715–724. doi:10.1016/j.carbon.2015.08.107.

R. Manoj Kumar, S.K. Sharma, B.V. Manoj Kumar, D. Lahiri, Effects of carbon

SC

[15]

nanotube aspect ratio on strengthening and tribological behavior of ultra high molecular

M AN U

weight polyethylene composite, Compos. Part A Appl. Sci. Manuf. 76 (2015) 62–72. doi:10.1016/j.compositesa.2015.05.007. [16]

B.

Arash,

Q.

Wang,

V.K.

Varadan,

Mechanical

properties

of

carbon

nanotube/polymer composites., Nature. (2014) 1–8. doi:10.1038/srep06479. [17]

L. Jin, C. Bower, O. Zhou, Alignment of carbon nanotubes in a polymer matrix by

[18]

TE D

mechanical stretching, Appl. Phys. Lett. 73 (1998).

E.T. Thostenson, T.-W. Chou, Aligned multi-walled carbon nanotube-reinforced

composites: processing and mechanical characterization, J. Phys. D. Appl. Phys. 35 (2002)

[19]

EP

L77. http://stacks.iop.org/0022-3727/35/i=16/a=103. Y. Zhang, S. Iijima, Formation of single-wall carbon nanotubes by laser ablation of

[20]

AC C

fullerenes at low temperature, Appl. Phys. Lett. 75 (1999). R. Haggenmueller, H.H. Gommans, a. G. Rinzler, J.E. Fischer, K.I. Winey, Aligned

single-wall carbon nanotubes in composites by melt processing methods, Chem. Phys. Lett. 330 (2000) 219–225. doi:10.1016/S0009-2614(00)01013-7. [21]

C.K. Najeeb, J. Chang, J.-H. Lee, J.-H. Kim, Fabrication of aligned ultra-thin

transparent conductive films of single-walled carbon nanotubes by a compression/sliding method,

Scr.

Mater.

64

(2011)

126–129.

doi:http://dx.doi.org/10.1016/j.scriptamat.2010.09.024.

23

ACCEPTED MANUSCRIPT [22]

C. Ma, H.-Y. Liu, X. Du, L. Mach, F. Xu, Y.-W. Mai, Fracture resistance, thermal

and electrical properties of epoxy composites containing aligned carbon nanotubes by low magnetic

field,

Compos.

Sci.

Technol.

114

(2015)

126–135.

doi:http://dx.doi.org/10.1016/j.compscitech.2015.04.007. [23]

B.W. Smith, B.W. Smith, Z. Benes, Z. Benes, D.E. Luzzi, D.E. Luzzi, et al.,

RI PT

Structural anisotropy of magnetically aligned single wall carbon nanotube films, Appl. Phys. Lett. 77 (2000) 663–665. doi:10.1063/1.127078. [24]

M.J. Casavant, D.A. Walters, J.J. Schmidt, R.E. Smalley, Neat macroscopic

[25]

SC

membranes of aligned carbon nanotubes, J. Appl. Phys. 93 (2003).

J.E. Fischer, W. Zhou, J. Vavro, M.C. Llaguno, C. Guthy, R. Haggenmueller, et al.,

M AN U

Magnetically aligned single wall carbon nanotube films: Preferred orientation and anisotropic transport properties, J. Appl. Phys. 93 (2003). [26]

Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis, Carbon nanotube-polymer

composites: Chemistry, processing, mechanical and electrical properties, Prog. Polym. Sci. 35 (2010) 357–401. doi:10.1016/j.progpolymsci.2009.09.003.

T. Kimura, H. Ago, M. Tobita, S. Ohshima, M. Kyotani, M. Yumura, Polymer

TE D

[27]

composites of carbon nanotubes aligned by a magnetic field, Adv. Mater. 14 (2002) 1380– 1383. doi:10.1002/1521-4095(20021002)14:19<1380::AID-ADMA1380>3.0.CO;2-V. K.

Prabakaran,

A.K.

Palai,

S.

Mohanty,

S.K.

Nayak,

Aligned

carbon

EP

[28]

nanotube/polymer hybrid electrolytes for high performance dye sensitized solar cell

[29]

AC C

applications, RSC Adv. 5 (2015) 66563–66574. doi:10.1039/C5RA10843H. M. Arguin, F. Sirois, D. Therriault, Electric field induced alignment of multiwalled

carbon nanotubes in polymers and multiscale composites, Adv. Manuf. Polym. Compos. Sci. 1 (2015) 16–25. doi:10.1179/2055035914Y.0000000003. [30]

† Ralph Krupke *, † Frank Hennrich, ‡ Manfred M. Kappes †, ǁ and Hilbert v.

Löhneysen§, Surface Conductance Induced Dielectrophoresis of Semiconducting SingleWalled Carbon Nanotubes, Nano Lett. 4 (2004) 1395–1399. doi:10.1021/nl0493794.

24

ACCEPTED MANUSCRIPT [31]

X. Liu, J.L. Spencer, A.B. Kaiser, W.M. Arnold, Electric-field oriented carbon

nanotubes in different dielectric solvents, Curr. Appl. Phys. 4 (2004) 125–128. doi:10.1016/j.cap.2003.10.012. [32]

C. Chen, Y. Zhang, Manipulation of single-wall carbon nanotubes into dispersively

aligned arrays between metal electrodes, J. Phys. D. Appl. Phys. 39 (2006) 172.

[33]

RI PT

http://stacks.iop.org/0022-3727/39/i=1/a=025.

Zhuo Chen, † Yanlian Yang, Fang Chen, Quan Qing, Zhongyun Wu, and Zhongfan

Liu*, Controllable Interconnection of Single-Walled Carbon Nanotubes under AC Electric

[34]

SC

Field, J. Phys. Chem. B. 109 (2005) 11420–11423. doi:10.1021/jp051848i.

C. a. Martin, J.K.W. Sandler, a. H. Windle, M.-K. Schwarz, W. Bauhofer, K. Schulte,

M AN U

et al., Electric field-induced aligned multi-wall carbon nanotube networks in epoxy composites, Polymer (Guildf). 46 (2005) 877–886. doi:10.1016/j.polymer.2004.11.081. [35]

† ‡ Prashant V. Kamat *, ǁ K. George Thomas †, † Said Barazzouk, † G. Girishkumar,

§. K. Vinodgopal †, ‡ and Dan Meisel†, Self-Assembled Linear Bundles of Single Wall Carbon Nanotubes and Their Alignment and Deposition as a Film in a dc Field, J. Am. Chem.

[36]

TE D

Soc. 126 (2004) 10757–10762. doi:10.1021/ja0479888.

R.-P. Zhang, Y.-F. Zhu, C. Ma, J. Liang, Alignment of carbon nanotubes in

poly(methyl methacrylate) composites induced by electric field., J. Nanosci. Nanotechnol. 9

[37]

EP

(2009) 2887–2893.

C. Ma, W. Zhang, Y. Zhu, L. Ji, R. Zhang, N. Koratkar, et al., Alignment and

dispersion of functionalized carbon nanotubes in polymer composites induced by an electric

[38]

AC C

field, Carbon N. Y. 46 (2008) 706–710. doi:10.1016/j.carbon.2008.01.019. Y.-F. Zhu, C. Ma, W. Zhang, R.-P. Zhang, N. Koratkar, J. Liang, Alignment of

multiwalled carbon nanotubes in bulk epoxy composites via electric field, J. Appl. Phys. 105 (2009). doi:http://dx.doi.org/10.1063/1.3080243. [39]

R.J. Castellano, C. Akin, G. Giraldo, S. Kim, F. Fornasiero, J.W. Shan,

Electrokinetics of scalable, electric-field-assisted fabrication of vertically aligned carbonnanotube/polymer

composites,

J.

Appl.

Phys.

117

(2015).

doi:http://dx.doi.org/10.1063/1.4921948.

25

ACCEPTED MANUSCRIPT [40]

B. Vigolo,

a Pénicaud, C. Coulon, C. Sauder, R. Pailler, C. Journet, et al.,

Macroscopic fibers and ribbons of oriented carbon nanotubes., Science. 290 (2000) 1331– 1334. doi:10.1126/science.290.5495.1331. [41]

F. Ko, Y. Gogotsi, A. Ali, N. Naguib, H. Ye, G. Yang, et al., Electrospinning of

continuous carbon nanotube-filled nanofiber yarns, Adv. Mater. 15 (2003) 1161–1165.

[42]

RI PT

doi:10.1002/adma.200304955.

R. Sen, B. Zhao, D. Perea, M.E. Itkis, H. Hu, J. Love, et al., Preparation of single-

walled carbon nanotube reinforced polystyrene and polyurethane nanofibers and membranes

[43]

H. Search, C. Journals, A. Contact, M. Iopscience, I.P. Address, Orientation of

M AN U

Carbon Nanotubes Using Electrophoresis, 917 (n.d.). [44]

SC

by electrospinning, Nano Lett. 4 (2004) 459–464. doi:10.1021/nl035135s.

V. Sosa, F. Avile, Electrical and piezoresistive properties of multi-walled carbon

nanotube / polymer composite films aligned by an electric field, 9 (2011). doi:10.1016/j.carbon.2011.03.017. [45]

K. Yamamoto, S. Akita, Y. Nakayama, Orientation and purification of carbon

TE D

nanotubes using ac electrophoresis, J. Phys. D. Appl. Phys. 31 (1998) L34. http://stacks.iop.org/0022-3727/31/i=8/a=002. [46]

M. Monti, M. Natali, L. Torre, J.M. Kenny, The alignment of single walled carbon

EP

nanotubes in an epoxy resin by applying a {DC} electric field, Carbon N. Y. 50 (2012) 2453– 2464. doi:http://dx.doi.org/10.1016/j.carbon.2012.01.067. M. Senthil Kumar, T.H. Kim, S.H. Lee, S.M. Song, J.W. Yang, K.S. Nahm, et al.,

AC C

[47]

Influence of electric field type on the assembly of single walled carbon nanotubes, Chem. Phys. Lett. 383 (2004) 235–239. doi:10.1016/j.cplett.2003.11.032. [48]

a I. Oliva-Avilés, F. Avilés, V. Sosa, a I. Oliva, F. Gamboa, Dynamics of carbon

nanotube

alignment

by

electric

fields.,

Nanotechnology.

23

(2012)

465710.

doi:10.1088/0957-4484/23/46/465710. [49]

C. Park, J. Wilkinson, S. Banda, Z. Ounaies, K.E. Wise, G. Sauti, et al., Aligned

Single-Wall Carbon Nanotube Polymer Composites Using an Electric Field, (2006) 1751– 1762. doi:10.1002/polb. 26

ACCEPTED MANUSCRIPT [50]

T. Prasse, Electric anisotropy of carbon nanofibre/epoxy resin composites due to

electric field induced alignment, Compos. Sci. Technol. 63 (2003) 1835–1841. doi:10.1016/S0266-3538(03)00019-8. [51]

I.Ñ.Z. Alakain, S.I.G. Oyanes, I.Ñ.M. Ondragon, ELECTRIC FIELD ALIGNMENT

OF MULTI-WALLED CARBON NANOTUBES THROUGH CURING OF AN EPOXY

[52]

RI PT

MATRIX, (2012) 89–93.

Q. Wang, J. Dai, W. Li, Z. Wei, J. Jiang, The effects of CNT alignment on electrical

conductivity and mechanical properties of SWNT/epoxy nanocomposites, Compos. Sci.

[53]

SC

Technol. 68 (2008) 1644–1648. doi:10.1016/j.compscitech.2008.02.024.

J. Yu, R. Qian, P. Jiang, Enhanced thermal conductivity for PVDF composites with a

1323. doi:10.1007/s12221-013-1317-7. [54]

M AN U

hybrid functionalized graphene sheet-nanodiamond filler, Fibers Polym. 14 (2013) 1317–

S. Berber, Y. Kwon, D. Tomanek, Unusually high thermal conductivity of carbon

nanotubes, Phys. Rev. Lett. 84 (2000) 4613–6. doi:10.1103/PhysRevLett.84.4613. [55]

X. Benedict, S.G. Louie, M.L. Cohen, Static Polarizabilities of single-walled carbon Phys.

Rev.

B.

52

(1995)

8541–8549.

TE D

nanotubes,

doi:http://dx.doi.org/10.1103/PhysRevB.52.8541. [56]

D.S. Bychanok, M. V. Shuba, P.P. Kuzhir, S. a. Maksimenko, V. V. Kubarev, M. a.

EP

Kanygin, et al., Anisotropic electromagnetic properties of polymer composites containing oriented multiwall carbon nanotubes in respect to terahertz polarizer applications, J. Appl.

[57]

AC C

Phys. 114 (2013) 114304. doi:10.1063/1.4821773. W. Bauhofer, J.Z. Kovacs, A review and analysis of electrical percolation in carbon

nanotube

polymer

composites,

Compos.

Sci.

Technol.

69

(2009)

1486–1498.

doi:10.1016/j.compscitech.2008.06.018. [58]

T.W. Ebbesen, H.J. Lezec, H. Hiura, J.W. Bennett, H.F. Ghaemi, T. Thio, Electrical

conductivity

of

individual

carbon

nanotubes,

Nature.

382

(1996)

54–56.

http://dx.doi.org/10.1038/382054a0. [59]

M.M. Larijani, E.J. Khamse, Z. Asadollahi, M. Asadi, Effect of aligned carbon

nanotubes on electrical conductivity behaviour in polycarbonate matrix, 35 (2012) 305–311. 27

ACCEPTED MANUSCRIPT [60]

W. Guo, C. Liu, X. Sun, Z. Yang, H.G. Kia, H. Peng, Aligned carbon

nanotube/polymer composite fibers with improved mechanical strength and electrical conductivity, J. Mater. Chem. 22 (2012) 903. doi:10.1039/c1jm13769g. [61]

R.H. Baughman, A. a Zakhidov, W. a de Heer, Carbon nanotubes --- the route toward

[62]

RI PT

applications, Science (80-. ). 297 (2002) 787–92. doi:10.1126/science.1060928. L.J. Lanticse, Y. Tanabe, K. Matsui, Y. Kaburagi, K. Suda, M. Hoteida, et al., Shear-

induced preferential alignment of carbon nanotubes resulted in anisotropic electrical conductivity

of

polymer

composites,

Carbon

[63]

Y.

44

(2006)

3078–3086.

SC

doi:10.1016/j.carbon.2006.05.008.

N.

P. Pötschke, S.M. Dudkin, I. Alig, Dielectric spectroscopy on melt processed

M AN U

polycarbonate - Multiwalled carbon nanotube composites, Polymer (Guildf). 44 (2003) 5023– 5030. doi:10.1016/S0032-3861(03)00451-8. [64]

J.R. Wood, Q. Zhao, H.D. Wagner, Orientation of carbon nanotubes in polymers and

its detection by Raman spectroscopy, Compos. Part A Appl. Sci. Manuf. 32 (2001) 391–399. doi:10.1016/S1359-835X(00)00105-6.

Q. Jiang, X. Wang, Y. Zhu, D. Hui, Y. Qiu, Mechanical, electrical and thermal

TE D

[65]

properties of aligned carbon nanotube/polyimide composites, Compos. Part B Eng. 56 (2014) 408–412. doi:10.1016/j.compositesb.2013.08.064. T. Liu, I.Y. Phang, L. Shen, S.Y. Chow, W. De Zhang, Morphology and mechanical

EP

[66]

properties of multiwalled carbon nanotubes reinforced nylon-6 composites, Macromolecules.

[67]

AC C

37 (2004) 7214–7222. doi:10.1021/ma049132t. D. Qian, E. Dickey, R. Andrews, T. Rantell, Load transfer and deformation

mechanisms in carbon nanotube-polystyrene composites, Appl. Phys. Lett. 2868 (2000) 4–7. doi:10.1063/1.126500. [68]

J.N. Coleman, U. Khan, W.J. Blau, Y.K. Gun’ko, Small but strong: A review of the

mechanical properties of carbon nanotube-polymer composites, Carbon N. Y. 44 (2006) 1624–1652. doi:10.1016/j.carbon.2006.02.038. [69]

J. Wiley, Fundamentals of Materials Science and Engineering An Interactive, 2001.

28

ACCEPTED MANUSCRIPT Highlights

AC C

EP

TE D

M AN U

SC

RI PT


Alternating voltage and current assisted CNT alignment in polymer matrix was achieved
Mechanical and electrical properties of polymer were anisotropically enhanced with alignment
Current assisted alignment showed higher anisotropic conductivity as compared to voltage