Monte Carlo simulation of ion transport of the high strain ionomer with conducting powder electrodes

摘要

The transport of charge due to electric stimulus is the primary mechanism of actuation for a class of polymeric active materials known as ionomeric polymer transducers (IPT). At low frequency, strain response is strongly related to charge accumulation at the electrodes. Experimental results demonstrated using conducting powder, such as single-walled carbon nanotubes (SWNT), polyaniline (PANI) powders, high surface area RuO2, carbon black electrodes etc. as an electrode increases the mechanical deformation of the IPT by increasing the capacitance of the material. In this paper, Monte Carlo simulation of a two-dimensional ion hopping model has been built to describe ion transport in the IPT. The shape of the conducting powder is assumed to be a sphere. A step voltage is applied between the electrodes of the IPT, causing the thermally-activated hopping between multiwell energy structures. Energy barrier height includes three parts: the energy height due to the external electric potential, intrinsic energy, and the energy height due to ion interactions. Finite element method software-ANSYS is employed to calculate the static electric potential distribution inside the material with the powder sphere in varied locations. The interaction between ions and the electrodes including powder electrodes is determined by using the method of images. At each simulation step, the energy of each cation is updated to compute ion hopping rate which directly relates to the probability of an ion moving to its neighboring site. Simulation ends when the current drops to constant zero. Periodic boundary conditions are applied when ions hop in the direction perpendicular to the external electric field. When an ion is moved out of the simulation region, its corresponding periodic replica enters from the opposite side. In the direction of the external electric field, parallel programming is achieved in C augmented with functions that perform message-passing between processors using Message Passing Interface (MPI) standard. The effects of conducting powder size, locations and amount are discussed by studying the stationary charge density plots and ion distribution plots.