Tailoring the frequency-dependent electrical conductivity and dielectric permittivity of CNT-polymer nanocomposites with nanosized particles

Abstract

Recent experiments have shown that addition of nanosized particles into the carbon nanotube (CNT) based polymer composites could enhance the electrical conductivity and dielectric permittivity of the nanocomposites, but no theory seems to exist at present to quantify such influence. In this work, we develop a multi-scale effective-medium theory under the complex setting to study its effects over a wide range of AC frequency for a three-phase CNT-polymer-nanoparticle nanocomposite. In this process, the key issues of CNT and nanoparticle loading, particle-dependent dispersion state of CNTs, percolation threshold, electron tunneling, and Maxwell–Wagner–Sillars polarization, as well as the frequency-dependent Dyre electron hopping and Debye dielectric relaxation at the interface, are all considered. The developed theory is highlighted with a direct comparison to the experimental data of CNT-PVDF-nBaTiO3 nanocomposites over the frequency range from 102 to 107 Hz. It shows that, as AC frequency increases, the conductivity increases whereas the permittivity decreases. It also shows that, at an appropriate level of nanoparticle loading, the dispersion state improves, the percolation threshold decreases, and both conductivity and permittivity increase with nanoparticle loading. Beyond a critical level, the dispersed nanoparticles could start to have an adverse effect.