Spontaneous Emulsification of Triolein Induced by Mixed Micellar Solutions of Sodium Polyoxyethylene Alkyl Ether Sulfate and Dodecyldimethyl Amine Oxide.

A new mechanism of spontaneous emulsification without any salts or co-solvents is described, and is related to the dilatational behavior. Spontaneous emulsification can reduce the time required to remove oily soils from hard surfaces and enhance the detergency, because this type of emulsification requires no external mechanical work. In this paper, we focused on triolein, the main component of food oils and human sebum soil, and tried to induce spontaneous emulsification by using mixed micellar solutions of sodium polyoxyethylene alkyl ether sulfate and N, N-dimethyldodecylamine oxide (AES/DDAO). We characterized the dilatation of the oil/water interface using dynamic interfacial tension and elasticity measurements. This study confirmed that the degree of spontaneous emulsification can be enhanced by controlling the molar ratio of DDAO to AES. This enhancement can be attributed to an increased rate of decrease in the dynamic interfacial tension (i.e., a decreased interface dilatational elasticity), allowing for much greater suppression of the Marangoni effect. Further, we determined that one of the reasons for the decrease in the interface dilatational elasticity is the increasing number of micelles near the oil drop interface, which results from a decrease in the electrostatic repulsion between the micelles and the drop interface. Therefore, controlling the molar ratio of a mixed anionic/amphoteric surfactant solution is an effective way to induce spontaneous emulsification in the absence of salts or co-solvents.