Size-Polydisperse Model Ionic Liquid in Bulk

Abstract

The static and the dynamic properties of a sizepolydisperse model ionic liquid is studied using molecular dynamics simulations. Here, the size of the anions is derived from a Gaussian distribution while keeping cation size fixed, resulting in a system that closely corresponds to IL mixtures with a common cation. We systematically explore the behavior of thermodynamic transition temperatures, spatial ordering of ions, and the resulting screening behavior as a function of polydispersity index, δ. We observe a nonmonotonic dependence of transition temperatures on δ, and this nonmonotonic behavior is also reflected in other properties such as screening length. Furthermore, from the radial distribution function analysis it is found that, upon varying δ, the spatial ordering of cations is affected, while no such changes is seen for anion. On the other hand, the analysis of ion motion through mean-square displacement show that for all δ values considered both inertial and diffusive regimes are observed (as expected in the liquid state). However, in contrast to the neutral counterpart, the overall relaxation time of the polydisperse IL system increases (and hence decreasing diffusion coefficient) with increasing δ.

Effect of distribution shape on the melting transition, local ordering, and dynamics in a model size-polydisperse two-dimensional fluid

“…This effect has also been seen in studies of model ionic liquids in which particle size polydispersity varies in the anion. [48] This is because with small introduction of δ , the packing efficiency is greatly enhanced, as shown in Fig. 3 (φ ≈ 68.35% for 1C and ≈ 74% for G and U systems for δ ≈ 0.5% at T = 0.5).…”