Phase Separation in Nonaqueous Mixed Solvents Induced by Quaternary Ammonium Surfactants

When a quaternary ammonium surfactant has a suitable solubility in a polar solvent, it can induce the phase self-separation of mutually soluble polar and apolar mixed solvents and a stable interface between the two phases can be formed. This phenomenon is attributed to the quaternary ammonium surfactant reaching suitable solubility in the polar solvent and driving out the most part of the apolar solvent in which the surfactant is insoluble. As a result, phase separation appears. Using aqueous surfactant two-phase as reference, we suggest that it be termed nonaqueous surfactant two-phase and also as two oil phases for short.