Phase behavior of microemulsion systems based on optimized nonionic surfactants

Microemulsions can be obtained in different ways. For ethoxylated nonionic emulsifiers the temperature is the decisive parameter; therefore, the microemulsion phase is stable only in a certain limited temperature range. If other specific types of surfactants are used, e.g., alkyl polyglycosides, the temperature dependence is less pronounced or even negligible. In this case, the formation of microemulsions is enabled by adjusting a specific mixing ratio of different emulsifiers, i.e., balancing the hydrophilic to lipophilic components in the surfactant system. These effects have been studied for a variety of systems using mainly purified model raw materials. As microemulsions are gaining increasing importance for different applications, there is a need to study surfactants and surfactant mixtures that can be used in commercial products and to extend the knowledge to multicomponent emulsifier systems. In this study, the phase behavior of microemulsions consisting of alkyl polyglycosides and ethoxylates as hydrophilic emulsifiers, a lipophilic coemulsifier, an oily component, and water is evaluated in terms of microemulsion formation and stability. Parameters such as temperature, oil polarity, and composition of the surfactant mixture are discussed. It was shown that both the concentration range and the temperature stability could be extended by using suitable mixtures of emulsifiers and coemulsifiers.