Preparation of oil-in-water and water-in-oil emulsions with the same composition using hydrophilic nanoparticles by three-phase emulsification

This study was conducted to investigate whether oil-in-water (O/W) and water-in-oil (W/O) emulsions could be simultaneously obtained from the same raw materials via three-phase emulsification. The formation of both emulsion types was examined experimentally using the same hydrophilic nanoparticles and emulsion composition. Two different cases were considered. In the first case, only an O/W emulsion was formed, and in the other case, both O/W and W/O emulsions were produced depending on the interaction between nanoparticles and oil-water interface. These results were attributed to the location of hydrophilic nanoparticles at the oil-water interface. Only the O/W emulsion was obtained when nanoparticles were attached to the oil-water interface. Meanwhile, both types of emulsions were stably formed when nanoparticles partially penetrated the oil phase. Furthermore, even when the type of nanoparticles and emulsion composition were fully identical, the formation of both O/W and W/O emulsions could be independently controlled by varying the related non-thermodynamic parameters during preparation. For example, to produce the O/W emulsion, oil was added to the aqueous nanoparticle phase, and to prepare the W/O emulsion, the aqueous nanoparticle phase was poured into the oil phase. The findings of this work revealed that unlike conventional surfactant emulsification, the three-phase emulsification process mainly depended not on intensive parameters but on extensive parameters such as the masses and sizes of oil droplets and nanoparticles.