Influences of addition of hydrophilic surfactants on the W/O emulsions stabilized by lipophilic surfactants

Lipophilic surfactants were used in the oil/water system to form W/O emulsions, and the consequences of addition of hydrophilic surfactants to the emulsions were examined. The process was monitored by visual and microscopic observations and the droplet size as well as emulsion conductivity were determined. Multiple oil-in-water-in-oil (O/W/O) emulsions were observed when the hydrophilic surfactants concentrations were low. Surprisingly, the emulsion inverted to oil-in-water (O/W) when the concentrations of the hydrophilic surfactants were increased. The infrared (IR) spectrometer was also used to investigate the interesting phenomenon and the results demonstrated that the absorption changes of the hydroxyl groups and alkyl groups in IR spectra could effectively explain the morphologies changes. Morphological evolution of the emulsion with stirring time was applied to analyze the mechanism of the inversion of W/O to O/W.