Segregated carbon nanotube networks in CNT-polymer nanocomposites for higher electrical conductivity and dielectric permittivity, and lower percolation threshold

Abstract

In an effort to find higher electrical properties of CNT-based polymer composites, a segregated CNT (carbon nanotube) network model is constructed, and a computational scheme is also provided. The construction involves randomly oriented CNTs decorated on the surface of polymer particles. A two-scale computational scheme with segregated CNT networks as the small scale and the overall composite consisting of polymer particles and segregated networks as the large scale is proposed. The small-scale problem involves percolation feature and is solved through Bruggeman's effective-medium approximation, while the large-scale problem is solved with Hashin's exact approach in conjunction with the small-scale solution. The formulations are further extended to the complex domain for the analysis of frequency dependence under AC loading. In this process, the influence of interphase, electron tunneling, Maxwell-Wagner-Sillars polarization, Dyre's electron hopping, and Debye's dielectric relaxation, are also incorporated. The calculated results are validated with experimental data of 2-phase CNT/PA (polyamide) and 3-phase CNT/PA/PP (polypropylene) nanocomposites. Compared with homogeneously dispersed CNT systems, it is also demonstrated that segregated CNT networks can indeed lead to markedly higher conductivity and permittivity, and lower percolation threshold.