An empirical equation for electrical resistivity of thermoplastic polymer/multi-walled carbon nanotube composites

Industrial grade multi-walled carbon nanotubes (Nanocyl 7000) were incorporated into various thermoplastic polymers, such as polyamide 6, polyamide 11, polyamide 12, high-density polyethylene, polypropylene and polycarbonate, by a simple melt mixing process. An empirical equation has been fit to electrical measurements obtained by several experiments. The proposed empirical equation fit all of the experimental data above the percolation threshold concentration very well, and it has been proven that each parameter of the empirical equation has a strong correlation with the state of dispersion of the carbon nanotubes. Furthermore, for the first time, the Hansen solubility parameter has been used to predict compatibility between carbon nanotubes and thermoplastic polymers, and the predicted result strongly resembles data obtained in several other reports.     

Effect of styrene–acrylonitrile on the electrical resistivity of polycarbonate/multiwalled carbon nanotube composites

Multiwalled carbon nanotube (MWCNT)‐filled polycarbonate (PC)/styrene–acrylonitrile (SAN) blends with a wide range of blend compositions were prepared by melt mixing in a rotational rheometer, and the effect of SAN on the electrical properties of the PC/MWCNT composites was studied. The structure/electrical property relationship was investigated and explained by a combination of MWCNT localization and blend morphology. Transmission electron micrographs showed selective localization of MWCNTs in the PC phase, regardless of the blend morphology. When the SAN concentration was 10–40 wt %, which corresponded to sea‐island (10–30 wt %) and cocontinuous (40 wt %) blend morphologies (PC was continuous in both structures), the electrical resistivity decreased with increases in the SAN content. The concept of an effective volume concentration of MWCNTs was used to explain this effect. When the SAN concentration was 70 wt % or higher, the electrical resistivity was very high because MWCNTs were confined in the isolated PC particles. In addition, SAN was replaced by other polymers [polystyrene, methyl methacrylate/styrene, and poly(methyl methacrylate)]; these yielded similar blend morphologies and MWCNT localization and showed the generality of the concept of effective concentration in explaining a decrease in the electrical resistivity upon the addition of a second polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Modulation of electrical properties in single-walled carbon nanotube/conducting polymer composites

The preparation and electrical characterization of a new class of composite layers formed by dispersing single-walled carbon nanotubes (SWNT) in 1,8-diaminonaphthalene polymer, the poly(1,8-DAN), are described.The material was grown on the surface of Pt plates by electropolymerization of 1,8-diaminonaphthalene (1,8-DAN) monomer in the presence of nanotubes. This synthesis method allows the simultaneous deposition of both the host polymer matrix and the filler nanotubes. A series of composite films were prepared using untreated nanotubes as well as nanotubes treated with KOH, HNO₃ and HNO₃/H₂SO₄ solutions. The structural features of the nanotubes and of the films produced have been investigated using Raman spectroscopy. Insight into the nature of nanotube dispersion and nanotube-polymer association was gained by AFM and STM analysis and by FE-SEM inspection after removing the outermost portion of composite films.The charge transport in composite films is found to be strongly enhanced by the nanotube insertion. Depending on the SWNTs processing, currents up to 30 mA, higher by a factor of about 140 than those of the pure poly(1,8-DAN) films, were measured with an applied voltage of 250 mV.     

Synthesis and characterization of soluble multi-walled carbon nanotube/poly(organophosphazene) composites

Poor solubility of carbon nanotubes (CNTs) in water and organic solvents offers a significant problem for their applications. Macromolecules can be suitable solubilizing agents and a structural component of composite materials for CNTs. Several polymers were tested for the preparation of CNT dispersions. In this study, a poly[(4-pyridineoxy)(phenoxy)phosphazene] (3) was prepared by sequential treatment of poly(dichlorophosphazene) (2) with sodium 4-pyridineoxy and sodium phenoxide in THF. Multi-walled carbon nanotube/poly(organophosphazene) composites (f-MWCNT/PZS) with different feed ratios [R_feed = 1:1, 1:3, 1:5 and 1:10 (w/w)] were obtained by the treatment of the functionalized multi-walled carbon nanotube (f-MWCNT) with the protonated poly(organophosphazene) (PZS). Excellent dispersions of the f-MWCNT/PZS nanocomposites in water and common organic solvents were achieved. The influence of feed ratio on polymer coating and the stability of composites were investigated by thermal gravimetric analysis (TGA). f-MWCNT/PZS_1:5 nanocomposite was characterized by ³¹P, ¹H NMR, FTIR, XRD, EDX and Raman Spectroscopy. The morphologic characterizations of f-MWCNT/PZS_1:5 were carried out by HRTEM and SEM methods.     

Doped polyaniline/multi-walled carbon nanotube composites: Preparation, characterization and properties

This study reports the synthesis of doped polyaniline in its emeraldine salt form (PANI-ES) with carboxylic acid and acylchloride groups contained multi-walled carbon nanotubes (designated as c-MWNTs and a-MWNTs) by in situ polymerization. Both Raman spectra and HRTEM images indicate that carboxylic acid and acylchloride groups formed at both ends and on the sidewalls of the MWNTs. Based on the π-π* electron interaction between aniline monomers and functionalized MWNT and hydrogen bonding interaction between the amino groups of aniline monomers and the carboxylic acid/acylchloride groups of functionalized MWNT, aniline molecules were adsorbed and polymerized on the surface of MWNTs. Structural analysis by FESEM and HRTEM showed that PANI-ES/c-MWNT and PANI-ES/a-MWNT composites are core (c-MWNT or a-MWNT)- shell (doped-PANI-ES) tubular structures with diameters of several tens to hundreds of nanometers, depending on the PANI content. The conductivities of 0.5 wt% functionalized MWNT containing PANI-ES/c-MWNT and PANI-ES/a-MWNT composites are 60-70% higher than that of PANI without MWNT.     

Preparation and characterization of polyaniline/multi-walled carbon nanotube composites

This study describes the synthesis of doped polyaniline in its emeraldine salt form (PANI-ES) with carboxylic groups containing multi-walled carbon nanotubes (c-MWNTs) via in situ polymerization. Both Raman and FTIR spectra indicate that carboxylic acid groups formed at both ends and on the sidewalls of the MWNTs. Based on the π-π* electron interaction between aniline monomers and MWNT and hydrogen bonding interaction between the amino groups of aniline monomers and the carboxylic acid group of c-MWNT, aniline molecules were adsorbed and polymerized on the surface of MWNTs. Structural analysis using FESEM and HRTEM showed that PANI-ES/c-MWNT composites are core (c-MWNT)-shell (doped-PANI-ES) tubular structures with diameters of several tens to hundreds of nanometers, depending on the PANI content. The conductivities of these PANI-ES/c-MWNT composites are 50-70% higher than those of PANI without MWNT.     

Effect of carbon nanotube addition on friction coefficient of nanotubes/hydroxyapatite composites

Carbon nanotubes/hydroxyapatite (CNTs/HA) composites with different CNTs contents were synthesized by in situ method and were characterized by XRD, TEM and Raman spectroscopy. Friction coefficients of the composites were tested using UMT-2 friction tester. Effect of various factors including CNTs content, testing time and applied load on friction coefficient was carried out. Results show that the CNTs/HA composites exhibited lower friction coefficient than pure HA and their friction coefficients decreased with increase of CNTs content from 0 to 20 wt.%. Addition of CNTs in composite is beneficial to increase wear resistance of the CNTs/HA composite and to decrease its friction coefficient.     

On the mechanism of piezoresistivity of carbon nanotube polymer composites

Carbon nanotube (CNT) polymer composites exhibit strong nonlinear and asymmetric piezoresistivity about zero strain in tensile and compressive strain states. The existing models explain the characteristic qualitatively but not quantitatively. This paper attempts to understand the mechanisms of this piezoresistivity by developing a new 3-dimensional percolation CNT network model, where the effect of CNT deformation (wall indentation and tube bending) is considered for the first time. The predicted electrical conductivity and piezoresistivity agree with experiments quantitatively, which reveals that the CNT deformation is a dominant mechanism for the nonlinearity and asymmetry of piezoresistivity of CNT-polymer composites. Parametric studies have been conducted to show the effects of morphology and electrical properties of CNTs, work functions and Poisson's ratio of polymer on the piezoresistivity of CNT-polymer composites for future application in nanosensing composites.     

Experimental investigation of dispersion during flow of multi-walled carbon nanotube/polymer suspension in fibrous porous media

We prepared three types of multi-walled carbon nanotubes (MWNT)/vinyl ester resin suspensions with different degrees of initial MWNT dispersion. Each suspension was injected into a mold cavity to saturate a stationary random glass fiber preform. High shear rates were not encountered in the non-uniform porous media. The quality of dispersion of the MWNT caused by the interaction between the MWNT with glass fiber media was characterized by examining the sections of the cured composites using scanning electron microscope (SEM) and transmission electron microscope (TEM). The results revealed that the final MWNT/Glass fiber structure is a strong function of the initial state of the MWNT dispersion in the suspension and the porous media structure.     

Evaluation and identification of electrical and thermal conduction mechanisms in carbon nanotube/epoxy composites

Nanostructured modification of polymers has opened up new perspectives for multi-functional materials. In particular, carbon nanotubes (CNTs) have the potential to realise electrically conductive polymers with improved or retaining mechanical performance. This study focuses on the evaluation of both, the electrical and thermal conductivity of nanoparticulate filled epoxy resins. We discuss the results with regard to the influence of the type of carbon nanotube (SWCNT, DWCNT and MWCNT), the relevance of surface-functionalisation (amino-functionalisation), the influence of filler content (wt% and vol%), the varying dispersibility, the aspect ratio and the specific surface area.     

碳纳米管的制备及其聚合物基复合材料的研究进展

本文综述了单壁碳纳米管的制备方法,重点阐述了化学气相沉积法的合成运用,并对目前碳纳米管在聚合物基纳米复合材料方面的研究做了综合阐述。     

Polymer/carbon nanotube composites for liquid sensing: Model for electrical response characteristics

Electrically conductive polymer composites (CPCs) based on carbon nanotubes (CNTs) and polycarbonate were investigated regarding their electrical resistance change in different solvents like tetrahydrofuran, acetone, and ethyl acetate. CPCs containing 0.086 to 2.778 vol.% CNT were melt mixed using a twin-screw extruder under optimised conditions and subsequently compression-moulded.All sensing experiments revealed a resistance increase of CPCs having a U-shaped sample geometry during solvent immersion. Light microscopy investigations have shown that the diffusion of solvents into CPCs can be monitored in terms of a pronounced diffusion front, separating a swollen skin from the dry core. Based on this observed skin-core morphology, a model allowing the calculation of the time depending relative resistance change has been proposed considering several factors like diffusion parameters, composite characteristics, and geometrical values.Simulated response curves based on the model were compared with experimental data obtained on the CPCs and very good agreement was observed. Using this model the influence of CNT content and kind of solvent could be described exactly.     

Modeling of effective elastic properties for polymer based carbon nanotube composites

Effective elastic properties of the nanocomposites filled with carbon nanotubes (CNTs) are investigated by the asymptotic expansion homogenization (AEH) method. In order to implement the homogenization method, a control volume finite element method (CVFEM) is employed in contrast to the previous studies. It is assumed that the nanocomposites have geometric periodicity with respect to local length scale and the elastic properties of nanocomposites can be represented by those of the representative volume element (RVE). Random orientation of the CNTs embedded in the nanocomposites is considered by using the orientation tensor. The effective elasticity tensor predicted by the homogenization method is compared with analytical and experimental results. In the experiment, the CNT surface is treated by oxygen plasma to improve interfacial bonding between the CNT and the matrix and to disperse the CNTs homogeneously in epoxy resin because the perfect interfacial bonding is presumed in the homogenization method. Homogeneous CNT dispersion is experimentally identified by the field emission scanning electronic microscope (FESEM). It is found that the numerically calculated elastic modulus is in good agreement with that obtained by analytic model.     

Improved mechanical properties of carbon nanotube/polymer composites through the use of carboxyl-epoxide functional group linkages

Single-walled and multi-walled carbon nanotubes (CNTs) were functionalized with carboxyl groups and dispersed in a polymer containing an epoxide group. We have then observed experimentally that mutual chemical reaction between the functional groups on the CNTs with the polymer epoxide group can enhance, two-fold, both the tensile strength and elastic modulus, E, of single walled CNT/polymer composites. A simple model was formulated to understand the variation of E with CNT volume fraction, considering agglomeration effects as well. An increase in the work of fracture, obtained from the experimental stress-strain curves, was seen at low nanotube filling fractions and is presumably due to crack bridging of the polymer matrix by CNTs. The influence of CNT length and geometry on mechanical properties, along with the influences of electrical and mechanical percolation thresholds was considered.     

Evaluation of effective thermal conductivity for carbon nanotube/polymer composites using control volume finite element method

Effective thermal conductivity of the polymeric composites filled with carbon nanotubes (CNTs) is predicted by using the asymptotic expansion homogenization technique (AEH), which makes it possible to localize and homogenize a heterogeneous medium. In the present study, CNT embedded epoxy composites are taken into account as the heterogeneous system. The representative volume element (RVE) employed in the homogenization process is constructed by assuming that the CNTs are dispersed homogeneously in the polymer matrix. It is presumed that the RVE contains a single CNT and that there is no direct interaction between neighboring CNTs. The dispersion state of CNTs in the composites is morphologically characterized by the field emission scanning electronic microscope (FESEM). In order to consider the orientation state of CNTs, the bounding approach is adopted by using the orientation tensor. It is found that the numerically homogenized thermal conductivity is higher than that obtained by the analytic model. Predicted conductivities are also compared with experimental results as well as analytic results. The homogenization technique yields the effective thermal conductivity accordant with experimental results. In the case that a heterogeneous material has anisotropic properties or geometrical complexity, the homogenization technique is an efficient method to obtain averaged material properties equivalent to those of the real heterogeneous medium.     

Magnetic properties of multi-walled carbon nanotube-epoxy composites

Epoxy matrix composites have been prepared using as filler different weight fractions (0.03-1 wt%) of CVD grown multi-walled carbon nanotubes (MWCNTs) containing trapped iron nanoparticles. Magnetic characterization performed at room temperature with magnetic field between −19 and 19 kG shows that the nanocomposites are weakly ferromagnetic at room temperature. An abrupt variation in the dependence of both the coercivity field, B_C, and remanent magnetization, M_R, with the weight fraction of MWCNTs, ?, was found for ?=0.4%. Results suggest the formation of MWCNTs agglomerates for increasing weight concentrations, in accordance with SEM micrographs.