Mini-Review on Water-Oil Emulsions through Vibrational Sum Frequency Generation

Interfacial interactions between water and oil phases are present in various fields in which additives, such as surfactants, are utilized to minimize the surface stress between these phases to form an emulsion. However, the consequence of adding additives is not always easy to understand or to control due to the plethora of parameters that control the production of an emulsion phase. There are several macroscopic techniques to study the properties of emulsions. Nevertheless, these techniques cannot describe the mechanistic steps at the molecular level for interfaces with nanometer thicknesses. Among surface-sensitive techniques, vibrational sum frequency generation (VSFG) has been effectively utilized to study various parameters that control the formation of surfactant monolayers at water-oil interfaces. In this mini-review, a summary of molecular outputs by utilization of VSFG for studying the water-oil interfaces will be presented.