Insights into Tris-(2-Hydroxylethyl)methylammonium Methylsulfate Aqueous Solutions

Abstract

We report herein a combined experimental–computational study on tris-(2-hydroxylethyl)methylammonium methylsulfate in water solutions, as a representative ionic liquid of the aqueous-solution behavior of hydroxylammonium-based ionic liquids. Relevant thermophysical properties were measured as a function of mixture composition and temperature. Classical molecular dynamics simulations were performed to infer microscopic structural features. The reported results for ionic liquid in water-rich solutions show that it behaves as isolated non-interacting ions solvated by water molecules, through well-defined solvation shells, exerting a disrupting effect on the water hydrogen bonding network. Nevertheless, as ionic liquid concentration increase, interionic association increases, even for diluted water solutions, evolving from the typical behavior of strong electrolytes in solution toward large interacting structures. For ionic-liquid-rich mixtures, water exerts a minor disrupting effect on the fluid’s structuring because it occupies regions around each ion (developing water–ion hydrogen bonds) but without significantly weakening anion–cation interactions.