Ion-Pairing and Redissociation of Ionic Liquid

The properties of mixtures containing ionic liquid often exhibit interesting composition dependence like researches on electrical conductance. The unusual behavior was explained qualitatively based on the formation of dissociated ions in low IL concentrations and ion-pairs at high concentrations. The dissociation of IL is described as a chemical reaction (CA↔C⁺+A^-). In the dilute solution limit, ILs tends to fully dissociate. As the concentration of IL increases, some of the IL starts to associate and form ion-pairs. In some cases (e.g., water and acetonitrile as the solvent), the extent of ion-pairing of IL rises to a maximum at low concentration but then decreases monotonically as the concentration of IL approaches saturation. This breakup of ion-pairs depending on increase of concentration has been termed redissociation. In this work, such a redissociation phenomenon was investigated by using COSMO-SAC model.