Effect of the Temperature and Coordination Atom on the Physicochemical Properties of Chelate-Based Ionic Liquids and Their Binary Mixtures with Water

Abstract

Densities, viscosities, and conductivities of four chelate-based ionic liquids [Li(DOBA)][Tf2N], [Li(HDA)][Tf2N], [Li(DEA)][Tf2N], and [Li(EA)][Tf2N], and their binary mixtures with water were determined. Physical properties of [Li(DEA)][Tf2N], such as the thermal expansion coefficient of the ionic liquid, were calculated by empirical equations over a temperature range from 313.15 K to 333.15 K. The excess molar volume (VE) and viscosity deviations (Δη) were fitted by a Redlich–Kister equation. The excess molar volumes show a negative deviation from that of the ideal solution and two different behaviors between water-rich and IL-rich regions. Most viscosity deviations show negative values, except for that of the binary mixture of [Li(DOBA)][Tf2N]/water. The effect of chelate state on the above physicochemical properties has been discussed. Furthermore, the Walden rule was used to evaluate the relationship of molar conductivity and dynamic viscosity of these ionic liquid solutions, which indicates all of them have good ionicity.