Formation of fine emulsions by emulsification at high viscosity or low interfacial tension; A comparative study

This article deals with preparation of a model oil-in-water emulsion in a conventional stirred vessel using two energy efficient emulsification paths; emulsification at high viscosity (via concentrated emulsions) and emulsification at low interfacial tension. The first type of emulsification was carried out by addition of the oil (dispersed phase) to a small fraction of the water (continuous phase), while being stirred, followed by its dilution with the remainder of the water. The second type was carried out via phase inversion route by addition of the water to the oil. Drop rupturing was assisted by the high viscosity of the emulsion in the first method, but by the low interfacial tension of the emulsion in the second one. For the system under study, emulsification at high viscosity was found to be more efficient in producing fine droplets only if a low concentration of surfactant was used. Whereas with a high surfactant concentration, where an ultra-low interfacial tension was achievable, phase inversion emulsification produced finer droplets. The superiority of the methods, however, may change with the extent of shear. Both emulsification techniques revealed a sharp drop in their characteristic features including drop size, viscosity and interfacial tension below a certain concentration of the surfactant.