Properties of Surfactants: Emulsions

Despite the large number of chemical classes of surfactants,1 there are a limited number of functional attributes that make these materials of interest in formulations. It is these functional attributes of surfactants, a direct result of their amphiphilic nature, that are being examined in this series of articles. Formulators use surfactants for the functional properties they provide in products: conditioning, wetting, providing detergency and foam, and providing emulsifi cation.

Emulsification is a process that allows for the preparation of a metastable single phase of two insoluble materials. The metastable nature of the two insoluble materials is critical to understanding the nature and performance of emulsions. The metastable nature of the emulsion and the requirement that the emulsion be cosmetically appealing offer unique challenges to the formulator. This article will deal with the nature of the emulsion and what factors affect it.

During his Society of Cosmetic Chemists’ emulsion course, Ken Klein, an expert on emulsions, defi nes an emulsion as “a system of two or more immiscible materials, usually liquids, in which one material (the dispersed/internal phase) is suspended or dispersed throughout another material (the continuous/external phase) in separate droplets.” After having said this, Klein points out the admonition offered by Graham Barker, a wellknown expert in the fi eld of surfactants, who warns “all emulsions are inherently unstable, with the exception of spontaneously forming microemulsions. All we can do is delay the day when the instability will arrive.

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