Influence of co-surfactants on microemulsions with alkyl polyglycosides

Microemulsions are isotropic, thermodynamically stable systems consisting of surfactant, oil and water and, if necessary, additives such as alcohols or electrolytes. They can be obtained with emulsifier systems based on ethoxylated nonionic surfactants in a certain limited temperature range. If alkyl polyglycosides are used as surfactants, only a slight temperature dependence can be observed. In this case, the formation of microemulsions depends on the ratio of hydrophilic to lipophilic components in the surfactant system. Although there have been many studies regarding different oil/water/emulsifier systems, the formulation of microemulsions with optimal properties still depends on time-consuming empirical tests. The systematic investigation of the phase behavior of specifically selected systems is the basis for the development of emulsions for practical purposes. In this study, the phase behavior of model microemulsions consisting of an alkyl polyglycoside as hydrophilic emulsifier, a lipophilic co-emulsifier, an oil component and water is discussed. In particular the effects of different co-emulsifiers on the interface and therefore the formation and stability of microemulsions are assessed and interpreted. It turns out that an emulsifier system consisting of C-12/14 alkyl polyglycoside and glyceryl monooleate facilitates the formation of stable microemulsions very effectively. (C) 1998 Elsevier Science B.V. All rights reserved.