Tuning the miscibility of water in imide-based ionic liquids
Authors
A.S.L. Gouveia, C.E.S. Bernardes, A.S. Shaplov, E.I. Lozinskaya, J.N.C. Lopes, and I.M. Marrucho
Reference
Physical Chemistry Chemical Physics, vol. 42, no. 43, pp. 25236-25242, 2020
Description
Liquid-liquid phase behavior measurements were performed for binary mixtures of water and ionic liquids (ILs) containing the same 1-ethyl-3-methylimidazolium ([C(2)mim](+)) cation and different imide-based anions, having symmetric (bis(fluorosulfonyl)imide ([FSI](-))) or asymmetric structures (2,2,2-trifluoromethylsulfonyl-N-cyanoamide ([TFSAM](-)) and 2,2,2-trifluoro-N-(trifluoromethylsulfonyl)acetamide ([TSAC](-))). An inversion of phase behavior was observed: while below similar to 298 K, the miscibility of water in the studied ILs increases according to the order [C(2)mim][TSAC] < [C(2)mim][FSI] < [C(2)mim][NTf2], for temperatures above similar to 303 K, the reverse trend is observed [C(2)mim][NTf2] < [C(2)mim][FSI] < [C(2)mim][TSAC]. In turn, above similar to 306 K the [C(2)mim][TFSAM] is completely miscible with H2O in all ranges of concentrations. The obtained results also revealed an unusual water solubility variation of 11% in [C(2)mim][FSI], and 20% in [C(2)mim][TSAC], when the system temperature was changed by less than 1 K, around 298 K and 301 K, respectively. Molecular Dynamics (MD) simulations were used to understand the IL-water interactions and rationalize the experimental observations. These results suggested that the miscibility trends are mainly related to the ability of the water molecules to form water-anion and water-water aggregates in solution.
