Multiple-phase oil-in-water emulsions

Cosmetic oil-in-water emulsions such as lotions and creams are complex multiple-phase systems. In their preparation, combinations of fatty amphiphiles (glyceryl monoesters or fatty alcohols) and ionic or nonionic surfactants are widely used. The mixed emulsifier combinations interact in the aqueous continuous phases to form lameliar or crystalline structures. These both stabilise and sometimes control the consistencies of emulsions between wide limits. There is, however, confusion as to the type of lameliar phase that forms in a specific emulsion. The majority of the literature fails to distinguish between the lamellar liquid crystalline state and the equally important lamellar gel state. Although liquid crystalline phases form in many emul-sions at the high temperatures of manufacture, these often convert to gel phases when the emulsion cools so that the properties of this phase dominate the emulsion. In this article the structures and swelling properties of the different lameliar phases that occur in emulsions are discussed, as well as the formation of other crystalline phases. Attention is given to the conditions over which each type of phase forms and, in particular, the relevance of the gel-liquid crystalline transition temperature to emulsions. It will be shown how the behaviour of many complex emulsions during manu-facture, storage, and use can be related to the component phases