Physicochemical Characterization of Ionic Liquid Binary Mixtures Containing 1-Butyl-3-methylimidazolium as the Common Cation ^†

Mixing ionic liquids (as well as mixing an inorganic salt in an ionic liquid) constitutes an easy, elegant methodology for obtaining new ionic materials. In this study, 3 ionic liquids (ILs) sharing a common cation were synthesized and mixed in 9 different proportions giving rise to 27 binary mixtures. Specifically, 1-butyl-3-methylimidazolium nitrate, [C₄C₁Im][NO₃], 1-butyl-3-methylimidazolium chloride, [C₄C₁Im]Cl, and 1-butyl-3-methylimidazolium methanesulfonate, [C₄C₁Im][CH₃SO₃], were synthesized and characterized. They all share 1-butyl-3-methylimidazolium as the common archetypal cation. None of them (or any of their binary mixtures) is liquid at room temperature (T = 298.15 K), and two of them are only in the liquid state above temperatures of 343-353 K. Despite belonging to commonly used families of ILs, their handling and the study of their liquid properties (neat and mixtures) have become particularly difficult, mainly because of their tendency to solidify and their high viscosity (caused by hydrogen-bonded networks). The main goal of this work is to evaluate the thermal, dynamic, and volumetric properties of these compounds and their mixtures as well as the solid-liquid equilibria of their binary mixtures. Thermal properties, such as melting and glass-transition temperatures, were determined or calculated. Therefore, both density and viscosity have been measured and were used for the calculation of the isobaric thermal expansion coefficient, molar volumes, excess molar volumes, and viscosity deviations to linearity.