Effect of inorganic electrolytes on the formation and the stability of water-in-oil (W/O) emulsions

The phase inversion temperature (PIT) is an inherent property of many water/nonionic surfactant/oil systems. It tends to form O/W emulsions when the PIT is high and vice versa. In the present paper, formation of W/O emulsions was studied in aqueous/polyoxyethylene 4 lauryl ether/paraffinic oil systems by simply homogenizing. Polyoxyethylene 4 lauryl ether is a common hydrophilic surfactant and is normally used to produce O/W emulsions. Inorganic electrolyte species and their concentrations were appropriately chosen to reduce the PIT for the formation of W/O emulsions. Furthermore, the effects of surfactant concentration and oil/water phase volume ratio on the PIT were investigated by measuring the conductivity variation. Stability of W/O emulsions was studied as a function of inorganic electrolyte concentration and storage time by bottle test, microscope observation, and viscosity measurement, which shows that the sedimentation and coalescence lead to the destabilization of W/O emulsions.