| This dissertation comprises my research in spontaneous emulsification to produce thermodynamically unstable nano-emulsions. First, a new method to quantitatively determine the spontaneity of the emulsification process was designed. Second, with this method on hand, different factors affecting the drop size distribution and the mechanism of spontaneous emulsification were assessed (oil-chain-length, surfactant structure, surfactant-concentration, pH, salinity, synergism of surfactant mixtures). Third, it was shown that the presence (or formation and posterior destruction) of liquid crystal is an essential requirement for the formation of nano-emulsion with low energy consumption. Fourth, a correlation between spontaneous emulsification mechanism and drop size distribution was established. Here, it was shown that instabilities induced to the structures on self-assembled systems such that liquid crystal and bicontinuous microemulsion lead to the formation of emulsions with nano-size drops (<1 μm). On the other hand, instabilities induced to interfaces of the hydrodynamic kind such as Raleigh-like instabilities or interfacial turbulence lead to emulsion with large-drops (40–100μm). Furthermore, instabilities via diffusion and stranding produce emulsion with medium drop size (1 to 20μm). Fifth, it was shown that surfactant structure, surfactant concentration, and surfactant application protocol are the keys to spontaneously remove oil (soil) from polyester fabric. It was also shown that these factors control the main mechanisms (rollback and spontaneous emulsification) for spontaneous detergency of oil. Sixth, it was shown that the spontaneous emulsification and the molecular interaction at the interface and in bulk phases are key factors to consider for the removal of hazardous molecules (e.g., phenol) from water. Finally, it is important to stress the fact that nano-emulsions are very important systems in science as well as in technology and this research showed the mechanism and emulsification protocol to produce emulsions with different drop sizes including nano-size (nano-emulsion). |
