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j. Soc. Cosmet. Chem., 41, 23-49 (January/February 1990) Polymer/surfactant interaction E. D. GODDARD, Specialty Chemicals Division, Union Carbide Corporation, Tarrytown, NY 10591. Received November 21, 1989. Presented at the Annual Meeting of the Sodety of Cosmetic Chemists, New York, December 1989. Synopsis Water-soluble polymers and surfactants are common ingredients of cosmetic formulations that are known to influence each other's properties. This article reviews some of the methods that have been used to study polymer/surfactant pairs, lists the factors which influence their properties and interaction, and analyzes the factors responsible for this interaction. In addition, some opportunities afforded by the changes in proper- ties occasioned by these interactions are outlined. INTRODUCTION In cosmetic formulation and technology, use is made of a wide variety of surfactants and also of a number of different water-soluble polymers. It is, in fact, the case in many systems, e.g. shampoos, lotions, creams, dentifrices, and so on, that both of these species are present in the same system. In recent years a great deal of scientific study has been carried out on the properties of such mixtures in model systems (1-3). The present article seeks to summarize the high points of these studies, to identify features of these investigations relevant to cosmetic systems and, furthermore, to draw attention to opportunities for exploiting certain properties of these binary mixtures. It should be pointed out that interaction and complex formation between natural polymers (proteins) and "surfactants" (lipiris) were recognized a long time ago (4). This article will, how- ever, not deal with lipoproteins but will be concerned largely with synthetic polymers and synthetic surfactants. However, it should be recognized that many of the principles and properties described will be directly applicable to protein/surfactant pairs also. Before discussing mixed systems, it is appropriate to briefly describe the properties of each of these components when in aqueous solution, namely the properties of surfactant solutions and of polymer solutions. Such a discussion, in a general sense, will aid the understanding of what interaction can be expected when the two species are present in the same solution. SURFACTANTS A surfactant is the classical case of an amphipathic molecular structure. In aqueous solution the ionic headgroup, or the polar headgroup (e.g., polyoxyethylene group), 23