Computational Studies of Structures and Dynamics of 1,3-Dimethylimidazolim Salt Liquids and their Interfaces Using Polarizable Potential Models

Abstract

The structures, thermodynamics, and dynamical properties of bulk and air/liquid interfaces of three ionic liquids, 1,3-dimethylimidazolium [dmim](+) with Cl(-), Br(-), and I(-) were studied using molecular dynamics techniques and polarizable potential models. In bulk melts, the radial distribution functions reveal a significant long-range structural correlation in these ionic liquids. The single-ion dynamics are studied via mean-square-displacements, velocity and orientational correlation functions. We observe that anion size plays an important role in the dynamics of ionic liquids, with larger anions inducing faster cation and anion motion. The computed density profiles of the ionic liquid/vapor interface exhibit oscillatory behavior, indicative of surface layering at the interface. The computed surface tensions indicate small differences between these ionic liquids and decrease with the increasing anion size. The magnitudes of the computed potential drops of these ionic liquids are found to be small and negative and increase with the decreasing anion size. These results could imply that the cation dipoles on average orient more in the interfacial plane than perpendicular to it. Our results showed that anion type plays a major role in determining IL interfacial behavior.