Molecular Dynamics Simulations of Ammonium-Based Acrylate Polymerized Ionic Liquids

Abstract

Polymerized ionic liquids (polyILs) are interesting materials that may find application as the electrolyte in electrochemical devices provided that they can be made with sufficiently high ion conductivities. The continuous optimization requires the understanding of the ion transport in available materials. In this work, a group of ammonium-based acrylate polyILs were examined as the candidates with engineered side chains containing long linker and various alkyl tails. Classical molecular dynamics simulations were performed to investigate the mechanism of ion transport. For all simulated systems, the diffusion coefficients were higher than previously investigated polyILs with imidazolium vinyl cations directly bonded to the backbones. Diffusivity was further improved when the tail length increased from methyl to propyl, but this trend did not persist for butyl and longer tails. The higher diffusion coefficient generally coexisted with less ion pair association, lower dynamical heterogeneity, and suppressed string-like cooperative motion. It was affirmed that only a few counterions were fast-moving for effective hopping, and the counterions exhibited smoother motion in acrylate polyILs than the imidazolium-based polyIL with a shorter side chain. For better ion transport, this work suggested that long linker and intermediate tails in the polymerized ions appeared to be the attractive candidates.