Fundamental Differences in Emulsification Principle between Three-phase Emulsification and Conventional Methods

The present study investigates the principle difference between three-phase emulsification and conventional emulsification methods (surfactant emulsification and the Pickering method). Conventional emulsification methods depend on intensive factors such as interfacial tension and wetting. In the proposed three-phase emulsification, soft hydrophilic nanoparticles adhere to the oil-water interface due to the van der Waals attraction and stabilize the emulsion. Therefore, it can be said that three-phase emulsification is "extensive emulsification" based on the mass of the hydrophilic nanoparticles and oil droplets. Extensive emulsification is irreversible because the van der Waals attraction acts between the particles unless the mass of the soft hydrophilic nanoparticles and oil droplets changes. The differences between three-phase emulsification and conventional emulsification methods were experimentally verified by comparing the difference in the stability of the emulsions resulting from the change in intensive factors, where the internal phase oil transitioned from solid to liquid. The emulsions prepared using the surfactant and Pickering methods were separated into oil and water by the solid-liquid phase transition of hexadecane in the internal oil phase. However, the emulsion prepared using three-phase emulsification maintained its emulsified state without any oil-water separation even when the internal oil phase underwent solid-liquid phase transition. From the results obtained, it can be concluded that three-phase emulsification is an irreversible method because its mechanism is based on extensive factors. Furthermore, this irreversible method allows the emulsification of various oils that cannot be emulsified by conventional methods, and it is also possible to directly mix emulsions prepared with different oils. The authors also call attention to the possibility of improving emulsion characters and new developments in emulsion science.