Microemulsions stabilized by ionic/nonionic surfactant mixtures. Effect of partitioning of the nonionic surfactant into the oil

The properties of microemulsions stabilized by mixtures of the ionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and the nonionic surfactant pentaethylene glycol n-dodecyl ether (C12E5) were modeled and allowed independent optimization of both the temperature sensitive and temperature insensitive systems. The model was formulated in terms of the surfactant composition of the monolayers stabilizing the microemulsion aggregates. The model is extended to include the effect of partitioning of the nonionic surfactant from the mixed surfactant monolayers of the aggregates to the oil. The validity of the extended model is tested with phase inversion temperature measurements for AOT/C12E5 microemulsions.