The characteristics of carbon nanotube‐reinforced poly(phenylene sulfide) nanocomposites

Multiwall carbon nanotube reinforced poly (phenylene sulfide) (PPS) nanocomposites were successfully fabricated through melt compounding. Structural, electrical, thermal, rheological, and mechanical properties of the nanocomposites were systematically studied as a function of carbon nanotube (CNT) fraction. Electrical conductivity of the polymer was dramatically enhanced at low loading level of the nanotubes; the electrical percolation threshold lay between 1 and 2 wt % of the CNTs. Rheological properties of the PPS nanocomposites also showed a sudden change with the CNT fraction; the percolation threshold was in the range of 0–0.5 wt % of CNTs. The difference in electrical and rheological percolation threshold was mainly due to the different requirements needed in the carbon nanotube network in different stages. The crystallization and melting behavior of CNT‐filled PPS nanocomposites were studied with differential scanning calorimetry; no new crystalline form of PPS was observed in the nanocomposites, but the crystallization rate was reduced. The thermal and mechanical properties of the nanocomposites were also investigated, and both of them showed significant increase with CNT fraction. For 5 wt % of CNT‐filled PPS composite, the onset of degradation temperature increased by about 13.5°C, the modulus increased by about 33%, and tensile strength increased by about 172%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Surfactant‐assisted processing of polyimide/multiwall carbon nanotube nanocomposites for microelectronics applications

The dispersion and stability of carbon nanotubes (CNTs) inside a polymer matrix, especially with a high CNT content, are still big challenges. Moreover, the interaction between CNTs and the polymer matrix should be strong enough to improve the mechanical properties. The efficient dispersion of CNTs is essential for the formation of a uniform distribution of a CNT network in a polymer composite. Polyimide/multiwall CNT nanocomposites were synthesized by in situ polymerization with the aid of a surfactant. A Fourier transform infrared spectroscopy study proved that the surfactant did not hamper the polymerization of the polyimide. The microstructure, storage modulus and electrical conductivity of the nanocomposites were improved using a particular amount of the surfactant. Environmental stability test results showed that the polyimide with 1 wt% of CNTs produced with the aid of the surfactant possessed excellent reliability in high‐temperature and high‐humidity environments. Surfactants were successfully used to obtain fine‐structure polyimide/CNT nanocomposites by in situ polymerization. The enhancement of the mechanical properties was attributed to the incorporation of the surfactant. A percolation of electrical conductivity could be achieved with 1 wt% of CNTs. Copyright © 2010 Society of Chemical Industry     

Effect of carbon nanotube dispersion and network formation on thermal conductivity of thermoplastic polyurethane/carbon nanotube nanocomposites

Carbon nanotubes (CNTs) were dispersed without any solvent in poly(tetramethylene ether glycol), (PTMEG) well above its melting point by ultrasonication in the pulse mode and different times. The polyol/CNT suspensions were used to prepare in situ polymerized thermoplastic polyurethane TPU/CNT nanocomposites with the CNT concentration of ～ 0.05 vol%, much below the CNT geometrical percolation threshold calculated at 0.43 vol%. Results of rotational rheological measurements and ultraviolet–visible (UV‐Vis) spectroscopy analysis revealed improvement in the nanoscale CNT dispersion with sonication time. Moreover, the optical microscopic images and sedimentation behavior for these samples pointed out to the formation of segregated CNT networks with different microstructures at different sonication times. Through‐plane thermal conductivity measurements showed an increase in thermal conductivity of the in‐situ polymerized TPU/CNT nanocomposites from polyol/CNT suspensions with increasing sonication time followed by a decrease at long sonication times. Different models were used to evaluate the role of CNT dispersion state and created microstructure on thermal conductivity of nanocomposites. The formation of a segregated network at medium sonication times consisting of large CNT aggregates and small bundles increased the nanocomposite thermal conductivity up to 99.7%, while at longer sonication times, an increase in interfacial area with a corresponding increase in kapitza boundary resistance, effectively decreased the system thermal conductivity. POLYM. ENG. SCI., 56:394–407, 2016. © 2016 Society of Plastics Engineers     

Electrical and mechanical properties of carbon nanotube‐epoxy nanocomposites

In this work, electrical conductivity and thermo‐mechanical properties have been measured for carbon nanotube reinforced epoxy matrix composites. These nanocomposites consisted of two types of nanofillers, single walled carbon nanotubes (SW‐CNT) and electrical grade carbon nanotubes (XD‐CNT). The influence of the type of nanotubes and their corresponding loading weight fraction on the microstructure and the resulting electrical and mechanical properties of the nanocomposites have been investigated. The electrical conductivity of the nanocomposites showed a significantly high, about seven orders of magnitude, improvement at very low loading weight fractions of nanotubes in both types of nanocomposites. The percolation threshold in nanocomposites with SW‐CNT fillers was found to be around 0.015 wt % and that with XD‐CNT fillers around 0.0225 wt %. Transmission optical microscopy of the nanocomposites revealed some differences in the microstructure of the two types of nanocomposites which can be related to the variation in the percolation thresholds of these nanocomposites. The mechanical properties (storage modulus and loss modulus) and the glass transition temperature have not been compromised with the addition of fillers compared with significant enhancement of electrical properties. The main significance of these results is that XD‐CNTs can be used as a cost effective nanofiller for electrical applications of epoxy based nanocomposites at a fraction of SW‐CNT cost. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A facile route to develop electrical conductivity with minimum possible multi‐wall carbon nanotube (MWCNT) loading in poly(methyl methacrylate)/MWCNT nanocomposites

Today, we stand at the threshold of exploring carbon nanotube (CNT) based conducting polymer nanocomposites as a new paradigm for the next generation multifunctional materials. However, irrespective of the reported methods of composite preparation, the use of CNTs in most polymer matrices to date has been limited by challenges in processing and insufficient dispersability of CNTs without chemical functionalization. Thus, development of an industrially feasible process for preparation of polymer/CNT conducting nanocomposites at very low CNT loading is essential prior to the commercialization of polymer/CNT nanocomposites. Here, we demonstrate a process technology that involves in situ bulk polymerization of methyl methacrylate monomer in the presence of multi‐wall carbon nanotubes (MWCNTs) and commercial poly(methyl methacrylate) (PMMA) beads, for the preparation of PMMA/MWCNT conducting nanocomposites with significantly lower (0.12 wt% MWCNT) percolation threshold than ever reported with unmodified commercial CNTs of similar qualities. Thus, a conductivity of 4.71 × 10^?5 and 2.04 × 10^?3 S cm^?1 was achieved in the PMMA/MWCNT nanocomposites through a homogeneous dispersion of 0.2 and 0.4 wt% CNT, respectively, selectively in the in situ polymerized PMMA region by using 70 wt% PMMA beads during the polymerization. At a constant CNT loading, the conductivity of the composites was increased with increasing weight percentage of PMMA beads, indicating the formation of a more continuous network structure of the CNTs in the PMMA matrix. Scanning and transmission electron microscopy studies revealed the dispersion of MWCNTs selectively in the in situ polymerized PMMA phase of the nanocomposites. Copyright © 2012 Society of Chemical Industry     

Impact of injection‐molding processing parameters on the electrical,mechanical, and thermal properties of thermoplastic/carbon nanotube nanocomposites

Thermoplastic nanocomposites, based on high‐density polyethylene, polyamide 6, polyamide 66, poly(butylene terephthalate), or polycarbonate and containing multiwalled carbon nanotubes (CNTs), were compounded with either neat CNTs or commercial CNT master batches and injection‐molded for the evaluation of their electrical, mechanical, and thermal properties. The nanocomposites reached a percolation threshold within CNT concentrations of 2–5 wt %; however, the mechanical properties of the host polymers were affected. For some nanocomposites, better properties were achieved with neat CNTs, whereas for others, master batches were better. Then, polycarbonate and poly(butylene terephthalate), both with a CNT concentration of 3 wt %, were injection‐molded with a screening design of experiments (DOE) to evaluate the effects of the processing parameters on the properties of the nanocomposites. Although only a 10‐run screening DOE was performed, such effects were clearly observed. The volume resistivity was significantly dependent on the working temperature and varied up to 4 orders of magnitude. Other properties were also dependent on the processing parameters, albeit in a less pronounced fashion. Transmission electron microscopy indicated that conductive samples formed a percolation network, whereas nonconductive samples did not. In conclusion, injection‐molding parameters have a significant impact on the properties of polymer/CNT nanocomposites, and these parameters should be optimized to yield the best results. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology, structure and properties of conductive PS/CNT nanocomposite electrospun mat

The morphologies and properties of Polystyrene (PS)/Carbon Nanotube (CNT) conductive electrospun mat were studied in this paper. Nanocomposite fibers were obtained through electrospinning of PS/Di-Methyl Formamide (DMF) solution containing different concentrations and types of CNTs. The dispersion condition of CNTs was correlated to morphologies and properties of nanocomposite fibers. A copolymer as an interfacial agent (SBS, Styrene-butadiene-styrene type) was used to modify the dispersion of CNTs in PS solution before electrospinning. The results showed that the presence of the copolymer significantly enhances CNT dispersion. The fiber diameters varied between 200 nm and 800 nm depending on CNT type, polymer concentration and copolymer. The final morphological study of the fibers showed that CNT addition caused a decrease in beads formation along fiber axis before percolation threshold. However, addition of CNTs above percolation increased the beads formation, depending on the dispersion condition. The presence of SBS modified the dispersion, reduced the fiber diameter and the number of bead structures. Electrical conductivity measurements on nanocomposite mats of 15-300 μm in thickness showed an electrical percolation threshold around 4 wt% MWCNT; while the samples containing SBS showed higher values of conductivities below percolation compared to the samples with no compatibilizer. Enhancement in mechanical properties was observed by the addition of CNTs at concentrations below percolation.     

An Effective Strategy to Achieve Ultralow Electrical Percolation Threshold with CNTs Anchoring at the Interface of PVDF/PS Bi‐Continuous Structures to Form an Interfacial Conductive Layer

Conductive composites based on polymers and conductive nanofillers are widely studied as a promising material. The rational design of 3D conductive networks in composites is crucial to improve their electrical conductivity and reduce the dosage of nanofillers. Herein, poly(vinylidene fluoride) (PVDF) and polystyrene (PS) bi‐continuous structures with modified carbon nanotubes (CNTs) tailored to anchor at the interface are designed to achieve an ultralow electrical percolation threshold because of the formation of a thin interfacial conductive layer. In this work, the modification of CNTs with poly(methyl methacrylate) (PMMA), which contributes to the improvement of the compatibility between PVDF and CNTs, is effective to control the distribution of CNTs in composites. It promotes the migration of CNTs from the PS phase to the interface of PVDF and PS. Consequently, the interfacial conductive layer is formed at a low CNT content, and the electrical percolation threshold of PVDF/PS/CNTs‐PMMA nanocomposites is only 0.07 vol%, having a great decrease of about 50% compared with that of PVDF/PS/CNTs nanocomposites. Thus, it is demonstrated that the distribution of CNTs can be tailored to anchor at the interface by proper chemical modification to form an interfacial conductive layer and a decrease of percolation threshold can also be achieved.     

Studies on synergistic effect of CNT and CB nanoparticles on PVDF

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loading of carbon nanotubes (CNT) and carbon black (CB) were prepared by melt blending method. The conductivity and mechanical properties of the nanocomposites were investigated. The results showed that percolation threshold of CNT/CB/PVDF nanocomposites appeared at a lower concentration (1.25 vol% CNT) than that of CNT/PVDF (>2.08 vol% CNT). The tensile strength of CNT/CB/PVDF nanocomposites was also improved, with 32.1% increase compared to PVDF and 18.0% increase compared to CNT/PVDF at loading of 1.25 vol% CNT/0.96 vol% CB. To explore the synergistic effect of CNT and CB, nonisothermal crystallization and isothermal crystallization behaviors of PVDF and its nanocomposites were studied by differential scanning calorimetry, and the crystallization morphology of them was observed under the three dimensional digital microscope with the polarized model. The crystallization rate of PVDF was speeded up markedly because of heterogeneous nucleation effect of nanoparticles, and CNT and CB nanoparticles had a synergistic effect on nucleation. Polarized microscope observation confirmed that spherulite size of PVDF became smaller owing to the accelerating of crystallization, which influenced the distribution of nanoparticles. The dispersion of nanofillers in matrix was observed by scanning electron microscope. It was revealed that CB could make CNT disperse more evenly in the PVDF matrix. The synergies network of CNT and CB is suggested to build in matrix, which improved conductivity and mechanical properties of PVDF nanocomposites. POLYM. COMPOS., 36:2248–2254, 2015. © 2014 Society of Plastics Engineers     

Selective Laser Sintering 3D Printing: A Way to Construct 3D Electrically Conductive Segregated Network in Polymer Matrix

Selective laser sintering (SLS), which can directly turn 3D models into real objects, is employed to prepare the flexible thermoplastic polyurethane (TPU) conductor using self‐made carbon nanotubes (CNTs) wrapped TPU powders. The SLS printing, as a shear‐free and free‐flowing processing without compacting, provides a unique approach to construct conductive segregated networks of CNTs in the polymer matrix. The electrical conductivity for the SLS processed TPU/CNTs composite has a lower percolation threshold of 0.2 wt% and reaches ≈10⁻¹ S m⁻¹ at 1 wt% CNTs content, which is seven orders of magnitude higher than that of conventional injection‐molded TPU/CNTs composites at the same CNTs content. The 3D printed TPU/CNTs specimen can maintain good flexibility and durability, even after repeated bending for 1000 cycles, the electrical resistance can keep at a nearly constant value. The flexible conductive TPU/CNTs composite with complicated structures and shapes like porous piezoresistors can be easily obtained by this approach.     

Influence of dispersion states of carbon nanotubes on physical properties of epoxy nanocomposites

Effects of different dispersion states of carbon nanotubes (CNTs) on rheological, mechanical, electrical, and thermal properties of the epoxy nanocomposites were studied. The dispersion states were altered depending upon whether a solvent was employed or not. To characterize dispersion of the CNTs, field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) were used. It was found that the nanocomposites containing poorly dispersed CNTs exhibited higher storage modulus, loss modulus, and complex viscosity than ones with well dispersed CNTs. It means that the poorly dispersed CNTs/epoxy composites have, from a rheological point of view, a more solid-like behavior. Tensile strength and elongation at break of the nanocomposites with different dispersion of CNTs were measured. Both of the well and the poorly dispersed CNTs composites showed a percolation threshold of electrical conductivity at less than 0.5 wt.% CNTs loading and the former had higher electrical and thermal conductivities than the latter. Effects of the CNTs content on the physical properties were also examined experimentally. As loading of the CNTs increased, improved results were obtained. From the morphological observation by FESEM and TEM, it was found that when the solvent was not used in the CNTs dispersion process, aggregates of pristine CNTs remained in the nanocomposites.     

Structure and properties of polypropylene‐wrapped carbon nanotubes composite

By means of in situ graft method, polypropylene (PP)‐wrapped carbon nanotubes (CNTs) composite were prepared. Infrared spectroscopy (IR) results showed that there was covalent linkage between PP and CNTs via maleic anhydride (MAH) grafting. Owing to the uniform dispersion of CNTs and covalent adhesion between PP and CNTs, the tensile strength of PP‐wrapped CNTs composite was higher than that for neat PP by 110%, and a 74% increase as compared to the CNTs/PP (with the same CNTs content) composite. The further test showed a strong mechanical behavior with up to 113% increase in Young's modulus of the neat PP. Based on the uniform dispersion of CNTs, the electrical conductivity of PP‐wrapped CNTs composite increased sharply by up to seven orders of magnitude with 4 wt % CNT fillers. As a result, the volume resistivity was decreased with increase in the CNT content that could be governed in a percolation‐like power law with a relatively low percolation threshold. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of carbon nanotubes and interphase properties on the interfacial conductivity and electrical conductivity of polymer nanocomposites

L_c is the minimum length of carbon nanotubes (CNTs) required for efficient transfer of filler conductivity to polymer matrix in polymer CNT nanocomposites (PCNTs). In this work, L_c is correlated with the dimensions of the CNTs and the interphase thickness. Subsequently, the interfacial conductivity as well as the effective length and concentration of CNTs are expressed by CNT and interphase properties. Moreover, a simple model for the tunneling conductivity of PCNTs is developed with these effective terms. The impacts of all parameters on L_c, the interfacial conductivity, the fraction of CNTs in the networks and the conductivity of the PCNT are explained and justified. In addition, the predictions of the percolation threshold and conductivity are compared with the experimental results of several samples. The desirable values of interfacial conductivity are achieved by thin, short and super‐conductive CNTs, high waviness and a thick interphase. However, thin and long CNTs, low waviness, a thick interphase, poor tunneling resistivity due to the polymer matrix and a short tunneling distance advantageously affect the conductivity of PCNTs, because they produce large conductive networks. The predictions also show good agreement with the experimental measurements of percolation threshold and conductivity, which confirms the developed equations. © 2020 Society of Chemical Industry     

In situ preparation of polyimide/amino‐functionalized carbon nanotube composites and their properties

In order to improve the dispersion of carbon nanotubes (CNTs) in polyimide (PI) matrix and the interfacial interaction between CNTs and PI, 4,4′‐diaminodiphenyl ether (ODA)‐functionalized carbon nanotubes (CNTs‐ODA) were synthesized by oxidation and amidation reactions. The structures and morphologies of CNTs‐ODA were characterized using Fourier transform infrared spectrometer, transmission electron microscopy, and thermal gravimetric analysis. Then a series of polyimide/amino‐functionalized carbon nanotube (PI/CNT‐ODA) nanocomposites were prepared by in situ polymerization. CNTs‐ODA were homogeneously dispersed in PI matrix. The influence of CNT‐ODA content on mechanical properties of PI/CNT‐ODA nanocomposites was investigated. It was found that the mechanical properties of nanocomposites were enhanced with the increase in CNT‐ODA loading. When the content of CNTs‐ODA was 3 wt%, the tensile strength of PI/CNT‐ODA nanocomposites was up to 169.07 MPa (87.11% higher than that of neat PI). The modulus of PI/CNTs‐ODA was increased by 62.64%, while elongation at break was increased by 66.05%. The improvement of the mechanical properties of PI/CNT‐ODA nanocomposites were due to the strong chemical bond and interfacial interaction between CNTs‐ODA and PI matrix. POLYM. COMPOS., 35:1952–1959, 2014. © 2014 Society of Plastics Engineers     

Fabrication and electrical properties of CNT/PP conductive composites with low percolation threshold by solid state alloying

The carbon nanotube/polypropylene conductive composites with a percolation threshold as low as 0.25 wt% were fabricated by solid state alloying. This solid state alloying method uses the super‐high speed mechanical shearing (at 10,000 rpm) to process the entangled catalytically grown carbon nanotubes (CNTs) and the polymer matrix in solid state. The electrical properties of the nanocomposites and the structure and distribution of CNTs were investigated. The results indicated that via the shear‐intensive process, CNTs were truncated and dispersed effectively, and their length could be controlled properly to fully exert the advantage of high aspect ratios (length‐to‐diameter ratios). At the same time, a linear structure conductive network which may considerably lower the percolation threshold was also formed by this method. Moreover, the CNTs could be further dispersed under the action of thermo energy provided by increasing the processing temperature. The super‐high speed solid state alloying method is a favorable approach for the production of low percolation threshold conductive composites of CNTs filled high viscosity resins. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

The use of a carbon nanotube layer on a polyurethane multifilament substrate for monitoring strains as large as 400%

A noninvasive approach is used to fabricate electronically conductive and flexible polymer fibers by fixing carbon nanotube (CNT) networks as a thin layer on thermoplastic polyurethane (TPU) multifilaments. The anchoring of the CNT layer is achieved by partially embedding or penetrating CNTs from the dispersion into the swollen multifilament surface. Thus a stable and high conductivity (up to 10² S/m at 10 wt.% CNT loading) of the resulting CNTs–TPU fibers is realized while the mechanical properties of the TPU multifilament, especially the strain to failure of >1500%, are not affected by increasing the thickness of the CNT layer. Real time analysis of the resistance of the CNTs–TPU fibers during incremental tensile loading tests reveal that the increase of resistance as a function of the strain is attributed to stretching-induced deformation, alignment, and, at high strains, destruction of the conducting network. Moreover, the changes in resistance are highly reversible under cyclic stretching up to a strain deformation of 400%.     

Alignment and properties of carbon nanotube buckypaper/liquid crystalline polymer composites

Carbon nanotubes (CNTs) have been recognized as a potential superior reinforcement for high‐performance, multifunctional composites. However, non‐uniform CNT dispersion within the polymer matrix, the lack of adequate adhesion between the constituents of the composites, and lack of nanotube alignment have hindered significant improvements in composite performance. In this study, we present the development of a layer‐by‐layer assembly method to produce high mechanical performance and electrical conductivity CNT‐reinforced liquid crystalline polymer (LCP) composites using CNT sheets or buckypaper (BP) and self‐reinforcing polyphenylene resin, Parmax. The Parmax/BP composite morphology, X‐ray diffraction, mechanical, thermal, and electrical properties have been investigated. SEM observations and X‐ray diffraction demonstrate alignment of the CNTs due to flow‐induced orientational ordering of LCP chains. The tensile strength and Young's modulus of the Parmax/BP nanocomposites with 6.23 wt % multi‐walled carbon nanotube content were 390 MPa and 33 GPa, respectively, which were substantially improved when compared to the neat LCP. Noticeable improvements in the thermal stability and glass transition temperature with increasing CNT content due to the restriction in chain mobility imposed by the CNTs was demonstrated. Moreover, the electrical conductivity of the composites increased sharply to 100.23 S/cm (from approximately 10^?13 S/cm) with the addition of CNT BP. These results suggest that the developed approach would be an effective method to fabricate high‐performance, multifunctional CNT/LCP nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Carbon nanotube/polypropylene/polycarbonate conductive nanocomposite films: Preparation and characterization

In this study, CNT/PP/PC conductive composite films were prepared by compounding PP (polypropylene)/PC (polycarbonate) (1:1) and carbon nanotubes (CNT) using a physical blending and hot pressing method. Next, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and water contact angle measurement are conducted in order to characterize the properties of CNT/PP/PC conductive films. The results showed there is no chemical reaction inside the PP/PC composite film with the addition of CNT. Neither the CNT composite film containing 3 wt% nor the control film decomposed thermally within 220°C. The water contact angle increased from 88.5° for the control film to 110.99° for the composite film containing 3 wt% CNT. This indicates that the film has good thermal stability and hydrophobic properties. The percolation threshold was obtained when the content of CNT was 3 wt%, and the best conductivity of the CNT/PP/PC composite film was 5.53 S/m at this time. In order to improve the tensile properties of the film, a small amount of polyurethane (TPU) was added to the film, and the maximum tensile strength was 24.91 Mpa when the content of TPU was 6.7%. This study can provide a strategy for the practical application of flexible electronic devices.     

Micro‐contact reconstruction of adjacent carbon nanotubes in polymer matrix through annealing‐Induced relaxation of interfacial residual stress and strain

Thermoplastic polyurethane (TPU)/multi‐walled carbon nanotubes (CNT) nanocomposites were prepared by twin‐screw extrusion and micro injection molding. The electrical conductivity of micro injection molded polymer nanocomposites exhibits a low value and uneven distribution in the micromolded samples. Real‐time tracing of electrical conductivity was conducted to investigate the post thermal treatment on the electrical conductivity of microinjection molded composites. The results show that postmolding thermal treatment leads to a significant increase in the electrical conductivity by over three orders of magnitude for 5 wt % CNT‐filled TPU composites. In‐situ Transmission electron microscopy confirms the conductive CNT network does not change at the micron/sub‐micron scale during thermal treatment. TEM image analysis by a statistical method was used to determine the spatial distribution of CNT in the sample and showed that the average distance between adjacent CNT reduced slightly at the nanometer scale after postmolding thermal treatment. A new conductive mechanism is proposed to explain the enhancement of electrical conductivity after thermal treatment, i.e. micro‐contact reconstruction of adjacent CNT in the polymer matrix through annealing‐induced relaxation of interfacial residual stress and strain. Raman spectra and small angle X‐ray scattering curve of annealed samples provide supporting evidence for the proposed new conductive mechanism. The electron tunneling model was used to understand the effect of inter‐particle distance on the conductivity of polymer composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42416.