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TRANSPARENT EMULSIONS BY LLOYD I. OSIPO•V, B.S.* Presented March 6, !963, New York City ABSTRACT The formulation of clear cosmetic "lotions" and "gels" is discussed in terms of Schulman's theory of microemulsions. Conditions required for the preparation of these microemulsions include a metastable negative interfacial tension and a liquid condensed interphase. It is shown that conventional emulsifying agents of both nonionic and ionic types can be used to prepare these systems. Agents are selected to condense and to expand the interfacial film. When these materials are present in the proper proportions, as determined by a "titration" procedure, a transparent emulsion results. I. INTI•ODt:e•r•ON There appears to be a growing interest on the part of cosmetic chem- ists in transparent fluid and gel cosmetic products containing appreciable amounts of both oil and water. There are several reasons for this interest. First, the industry is constantly searching for new products that are both usefial and have cosmetic appeal. Certainly, a crystal-clear liquid or gel is elegant and has a different appearance from an opaque product. Second, the transparent products may have increased utility, because of the likeli- hood that absorption into the skin will be promoted by the extremely small size of the dispersed droplets. Third, for the formulator, there is the advantage that these systems are easily prepared, and they are thermo- dynamically stable. Further, they can be opacified, so that they look like conventional creams and lotions. Lanolin derivatives are commonly used to prepare transparent cosmetic products, with excellent results. The intent of this paper is to show that other emulsifying agents may also be used and to present a theoretical basis for the formulation of these products. Microemulsions The transparent fluid and visco-elastic systems under discussion are treated here as microemulsions. The nature of microemulsions and the conditions under which they will form have been discussed by Schulman and co-workers (1-3). However, it should not be assumed that this is * Foster D. Snell, Inc., New York ll, N.Y. 277