Holger Tesmann

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 C12/14 alkyl polyglycoside and glyceryl monooleate facilitates the formation of stable microemulsions very effectively.

Calculation of optimum emulsifier mixtures for phase inversion emulsification

The phase inversion emulsification is a convenient method of preparing fine‐disperse and long‐term stable oil‐in‐water emulsions, which are stabilized with nonionic emulsifiers. On the basis of EACN‐values (equivalent alkane carbon numbers) the calculation of phase inversion in concentrates (CAPICO) is possible, which yields emulsifier and oil mixing ratios corresponding to a given phase inversion temperature (PIT). The CAPICO‐method is illustrated for the example of a cosmetic oil‐in‐water lotion containing an oil mixture, glyceryl monostearate and a fatty alcohol ethoxylate. Of special interest is the influence of silicone oils on the PIT. At a constant emulsifier oil ratio the complete phase behaviour of this emulsion system is represented in a temperature/water content graph. Optimum emulsification results are obtained if during PIT emulsification a microemulsion or a lamellar phase is passed. The emulsions were characterized by particle sizing, and emulsion stability against sedimentation was evaluated by ultrasonic velocity changes. A fine‐disperse and long‐term stable oil‐in‐water emulsion was prepared by a time and energy‐saving two‐step hot‐cold process.