"Amphiphilic" Ionic Liquid in a Mixture of Nonionic Liquids: Theoretical Study

We use a Flory Huggins type approach to describe a two-phase system consisting of nonionic components A and B that are incompatible with each other and of an ionic liquid (IL). The anions and the cations of the IL are considered as independent components and are assumed to have different affinities for A and B. We show that an up to several hundreds molecules thick double electrostatic layer is formed by the IL at the phase boundary, and the surface tension of the boundary happens to be smaller in the case of the three-component system than in the case of a two-component system consisting of the components A and B only; i.e., the IL plays the role of a surfactant. We investigate by means of a numerical calculation the full range of possible IL concentrations in the bulk of the two phases and also consider analytically the case of the low IL concentrations. The results obtained by means of the two methods are in perfect agreement.