Heterogeneity in microstructures and dynamics of dicationic ionic liquids with symmetric and asymmetric cations

Abstract

In order to understand the role of cation symmetry in intra- and inter-molecular structures and dynamics of dicationic ionic liquids (DILs), we present the MD simulations and Voronoi tessellation analysis of two DILs including [C5(mim)2][NTf2]2 and [C5(tma)(mim)][NTf2]2. In this work, we systematically examined the effect of changing the electrostatic interactions on microheterogeneity (MH) by fixing the strength of the vdW interactions. The qualitative and quantitative analyses of the MH were explored through total/partial structure factors, heterogeneity order parameter (HOP) and domain analysis. Furthermore, radial distribution functions (RDFs), coordination numbers, spatial distribution functions (SDFs), neighborhood analysis of ions and combined distribution functions (CDFs) were calculated to determine the arrangement of the nearest neighboring ions. Local structural heterogeneity leads to local dynamical heterogeneity, which plays an important role in the applications related to ion transportation. To investigate dynamical heterogeneity, the mean square displacement, non-Gaussian parameter, van Hove correlation, and also the hydrogen bond, ion pair, ion cage and reorientation dynamics have been calculated. The results showed that the replacement of one imidazolium head of symmetrical [C5(mim)2]2+ cation with a trimethylammonium group shows significant effects on their structures and dynamics.