Chameleonic Behavior of Ionic Liquids and Its Impact on the Estimation of Solubility Parameters

The possibility of developing a scale for solubility parameters, with the purpose of predicting the performance and aiding the selection of ILs, was evaluated. For the estimation of solubility parameters, infinite-dilution activity coefficient data were used. The results allowed the identification of a curious behavior for ILs that seem to present more than one solubility parameter, acting as polar molecules in some situations and as nonpolar molecules in others, depending on the medium.

This behavior was confirmed by solubility measurements of [C4MIM][PF6] in solvent mixtures. In this work, the solubility parameters were also estimated from other properties, namely, viscosities and enthalpies of vaporization, and the relation between the various sets of solubility parameters is discussed.

The results obtained suggest that, given the complexity of IL molecules and their liquid phases, a one-dimensional scale for solubility parameters that is able to characterize these fluids is not feasible.