Study on the Thermodynamic\nProperties of Ionic Liquids\n1‑Hexyl-3-methylimidazolium Halide with Isopropanol Mixtures

In this work, densities\nand viscosities of the mixtures of ionic\nliquids (ILs) 1-hexyl-3-methylimidazolium halides ([C<sub>6</sub>mim]X,\nwhere X = Cl<sup>–</sup>, Br<sup>–</sup>, and I<sup>–</sup>) and isopropanol (IPA) were measured over the temperature\nranging from 288.15 to 323.15 K to investigate the influence of anions,\nIL concentration, and temperature on the physical properties of the\nmixtures of ([C<sub>6</sub>mim]X + IPA). Excess volumes (<i>V</i><sup><i>E</i></sup>) and viscosity deviations (<i>Δη</i>) were also calculated to study the nonideal\nbehavior of ([C<sub>6</sub>mim]X + IPA). The <i>V</i><sup><i>E</i></sup> and <i>Δη</i> values\nof ([C<sub>6</sub>mim]X + IPA) are negative over the whole compositional\nrange at all temperatures, indicating that IPA molecules preferentially\ncoordinate with IL ions to form more densely packed structures. In\naddition, the molar enthalpies of mixing (Δ<sub><i>mix</i></sub><i>H</i>) for the mixtures were determined under\n298.15 and 308.15 K, and the nonrandom two-liquid model along with\nthe Gibbs–Helmholtz equation was introduced to describe Δ<sub><i>mix</i></sub><i>H</i> for the studied systems.\nThe mixtures of ([C<sub>6</sub>mim]Br + IPA) and ([C<sub>6</sub>mim]I\n+ IPA) showed endothermic behavior within the full range of compositions,\nwhile the mixtures of ([C<sub>6</sub>mim]Cl + IPA) showed endothermic\nfirst and then changed to exothermic behavior with increasing IL mole\nfraction.