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.