Phase inversion in abnormal O/W/O emulsions: I. Effect of surfactant concentration

The catastrophic phase inversion of a model abnormal O/W/O emulsion of a system composed of polyisobutylene, water, and a water-soluble grade surfactant was studied. The experiments were started with water being fed to the mixing vessel containing polyisobutylene to form a W/O emulsion. As the water volume fraction (f(w)) increased, multiple oil-in-water-in-oil drops formed by inclusion of the oil from the continuous phase. An increase in the surfactant concentration reduced the size of the oil-in-water-in-oil drops but did not significantly affect the size of the water-in-oil droplets. It also increased the inclusion of the continuous phase into the dispersed phase and advanced phase inversion. The mechanism of inclusion transformed from drop deformation to drop coalescence with increasing surfactant concentration and f(w). After an inversion, the internal oil-in-water-in-oil droplets were released into the water-continuous phase, forming a substantial number of the drops in the inverted emulsion.