Phase Inversion in Liquid-Liquid Dispersions

Background In a system of two immiscible liquids, usually water (or an aqueous solution) and an organic liquid (e.g. an oil), there are two general types of dispersions which can be formed depending on the conditions of the system. A water-in-oil (W/O) dispersion is a dispersion formed when the aqueous phase is dispersed in the organic phase and an oil-in-water (O/W) dispersion is a dispersion which is formed when the organic phase is dispersed in the aqueous phase. Phase inversion is the phenomenon whereby the phases of a liquid-liquid dispersion interchange such that the dispersed phase spontaneously inverts to become the continuous phase and vice versa under conditions determined by the system properties, volume ratio and energy input. This is illustrated in Figure 1 below. Thus, by definition, the phase inversion point is the holdup of the dispersed phase for a system at which the transition occurs i.e. when the dispersed phase becomes the continuous phase after an infinitesimal change is made to the system’s properties, phase ratio or energy input.