Study on the Thermodynamic Properties of Ionic Liquids 1-Hexyl-3-methylimidazolium Halide with Isopropanol Mixtures

In this work, densities and viscosities of the mixtures of ionic liquids (ILs) 1-hexyl-3-methylimidazolium halides ([C(6)mim]X, where X = Cl-, Br-, and I-) and isopropanol (IPA) were measured over the temperature ranging from 288.15 to 323.15 K to investigate the influence of anions, IL concentration, and temperature on the physical properties of the mixtures of ([C(6)mim]X + IPA). Excess volumes (V-E) and viscosity deviations (Delta eta) were also calculated to study the nonideal behavior of ([C(6)mim]X + IPA). The V-E and Delta eta values of ([C(6)mim]X + IPA) are negative over the whole compositional range at all temperatures, indicating that IPA molecules preferentially coordinate with IL ions to form more densely packed structures. In addition, the molar enthalpies of mixing (Delta H-mix) for the mixtures were determined under 298.15 and 308.15 K, and the nonrandom two-liquid model along with the Gibbs-Helmholtz equation was introduced to describe Delta H-mix for the studied systems. The mixtures of ([C(6)mim]Br + IPA) and ([C(6)mim]I + IPA) showed endothermic behavior within the full range of compositions, while the mixtures of ([C(6)mim]Cl + IPA) showed endothermic first and then changed to exothermic behavior with increasing IL mole fraction.