Determining the Accuracy of Classical Force Fields for Ionic Liquids: Atomistic Simulation of the Thermodynamic and Transport Properties of 1-Ethyl-3-methylimidazolium Ethylsulfate ([emim][EtSO4]) and Its Mixtures with Water

Abstract

The ability of simple classical force fields to predict the structure and density of ionic liquids is now well-established. However, it is less clear how accurate such force fields are for a range of other pure and mixture properties of ionic liquids. In this work, a single classical force field is used to compute a wide range of thermodynamic and transport properties for the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]). In addition to liquid densities, the volumetric expansivity, heat capacity, enthalpy of vaporization, rotational relaxation time, self-diffusivity, shear viscosity, and thermal conductivity are computed at various temperatures for the pure ionic liquid. The density, excess molar volume, enthalpy of mixing, partial molar enthalpy, water solubility as a function of partial pressure, rotational relaxation time, self-diffusivity, shear viscosity, and thermal conductivity are also computed for mixtures that contain different concentrations of water at various temperatures. The agreement between simulations and experiment is fair for most properties, although deviations in enthalpy of mixing, viscosity, and self-diffusivity are often large. It is shown that much of the error for mixtures with water likely is due to neglect of the water polarizability, which results in too strong of an attraction between water and the [EtSO4] anion.