Phase Behavior and Nano-emulsion Formation by the Phase Inversion Temperature Method

Formation of oil-in-water nano-emulsions has been studied in the water/C̄12Ē4/isohexadecane system by the phase inversion temperature emulsification method. Emulsification started at the corresponding hydrophilic−lipophilic balance temperature, and then the samples were quickly cooled to 25 °C. The influence of phase behavior on nano-emulsion droplet size and stability has been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the smallest droplet sizes were produced in samples where the emulsification started in a bicontinuous microemulsion (D) phase region or in a two-phase region consisting of a microemulsion (D) and a liquid crystalline phase (Lα). Although the breakdown process of nano-emulsions could be attributed to the oil transference from the smaller to the bigger droplets, the increase in instability found with the increase in surfactant concentration may be related to the higher surfactant excess, favoring the oil micellar transport between the emulsion droplets.