Article 17 (Research paper)

Zuo et al., Thermodynamic Study of Ionic Liquid Mixtures of 1-Hexyl-3-methylimidazolium Halide and Dimethyl Sulfoxide. J. Chem. Eng. Data 2025, 70, 8, 3112–3122

ABSTRACT: This study measured densities and viscosities of ionic liquid (IL) mixtures comprising 1-hexyl-3-methylimidazolium halides ([C₆mim][Halide], where Halide = Cl^–, Br^–, and I^–) with dimethyl sulfoxide (DMSO) (288.15–323.15 K) and enthalpies of mixing (Δ_mixH) at 298.15 and 308.15 K. Excess volumes (V^E) and viscosity deviations (Δη) were calculated to investigate nonideal behavior. Negative VE values indicate the formation of dense structures dominated by packing effects. Δη values suggest DMSO disrupts cation–anion interactions, causing deviations from ideality. Consistently negative ΔmixH values confirm strong ion–solvent interactions, with ([C₆mim]I + DMSO) showing the most negative Δ_mixH values, attributed to stronger iodide–DMSO interactions and weaker cation–anion interactions. The nonrandom two-liquid model and Gibbs–Helmholtz equation successfully modeled Δ_mixH, yielding ARDs of 3.9%, 4.5%, and 3.2%, respectively. Qualitative analysis with cosolvents (H₂O, MeOH, IPA) reveals the influences of cosolvent and anion on mixture properties. In organic solvents, V^E and Δη trends correlate with solvent molar volume and polarity. Specific interactions lead to unique V^E variations in DMSO mixtures, whereas extensive hydrogen bonding causes abnormal V^E and Δη trends in aqueous IL mixtures. Δ_mixH variations reflect the competition between ion–solvent and cation–anion interactions, influenced by solvent dielectric constant, polarity, and anion size.