Understanding the Ionic Conduction in Dielectric Polymers at High Electric Fields Using Molecular Dynamics Simulations.

Abstract

Applying molecular dynamics, we have studied ionic transport in polyethylene at moderate and high electric fields. The ion mobility of a variety of species is calculated and compared with existing theories. It reveals that ion mobility starts to deviate from the Einstein relation and increase roughly linearly with field beyond 100 MV/m, which results in a superlinear increase of the ionic current at high field that is consistent with the experimental results. At high field, we argue that the accelerated ion molecule is able to facilitate the conformation change of the surrounding polymers through elastic scattering, which in turn accommodates its passage. The extent of the mobility enhancement depends on the mass and size of the ion molecule. The ion transport is a thermally activated process, but has smaller activation energy than diffusion due to the additional energy provided by the field.