Article 18 (Research paper)
Zuo et al., Experimental and theoretical study on ion association in [Hmim][halide] + methanol/dimethyl sulfoxide mixtures. Fluid Phase Equilibria 600 (2026) 114571
ABSTRACT: The electrical conductivities of 1-hexyl-3-methylimidazolium halides ([Hmim][halide], halide = Cl–, Br–, I–) were measured in methanol (MeOH) and dimethyl sulfoxide (DMSO) at dilute concentrations from 293.15 to 313.15 K, alongside liquid density measurements for parametrization. Molar conductivity (Λ) decreased with increasing IL concentration and decreasing temperature, with solvent effects predominating over those of anion size. Λ was higher in MeOH than in DMSO due to lower viscosity and greater ion dissociation of MeOH. Comparison with a previous study involving H2O, MeOH, DMSO, and isopropanol confirmed that solvent viscosity is the dominant factor influencing Λ at infinite dilution. At higher IL concentrations, Λ in MeOH fell below that in H2O, likely due to a reduced number of free ions and the formation of larger solvated ion complexes.
To analyze conductivity behavior, the Debye-Huckel-Onsager model was employed to determine the limiting molar conductivity (Λ0), which was subsequently used in the Shedlovsky equation to calculate the association constant (KA). For comparison, simultaneous regression of Λ0 and KA was also performed. The results indicated that, within the same solvent, Λ0 increased with temperature, while KA exhibited irregular trends. Across different solvents, Λ0 correlated with solvent viscosity, and KA was influenced by dielectric constant and polarity. Solvent effects on both Λ0 and KA were more pronounced than those of anion size, suggesting the dominant role of the solvent environment. Positive Eyring activation enthalpies showed the endothermic ion-pairing process. Additionally, the Walden product suggested stronger ion-solvent interactions and larger solvated ions in MeOH compared to DMSO. These findings provide deeper insight into IL conductivity in diverse solvent environments.