The tricyanomethanide anion favors low viscosity of the pure ionic liquid and its aqueous mixtures.

Abstract

Ionic liquids (ILs) constitute a broad research interest. One of the serious drawbacks of ILs is their high shear viscosity, which originates from bulky particles and strong cation-anion coordination. A continuous molecular design is being done to develop low-viscosity ILs. Low-viscosity ILs are also expected to exhibit an increased ionic conductivity. We investigate such an IL composed using a new anion (to the IL field) tricyanomethanide [C(CN)3](-) and the cation 1-ethyl-3-methylimidazolium [EMIM](+). Having developed the force field for [EMIM][C(CN)3], we simulate molecular dynamics (MD) of the pure IL and its mixtures with water over an entire range of compositions. According to MD simulations, [EMIM][C(CN)3] exhibits unusually low shear viscosity (for the imidazolium family) and high ionic conductivity. This is achieved thanks to weak cation-anion coordination and no hydrogen bonding between them. Furthermore, cation-water and anion-water hydrogen bonds were detected in the [EMIM][C(CN)3]/water mixtures. We correlate the structure and dynamics of [EMIM][C(CN)3] in aqueous mixtures to provide guidelines for future development of low-viscosity and highly conductive ILs.