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Cosmet. Sci., 49, 89-100 (March/April 1998) Evaporation-freezino and rheolooical behavior of silicone surfactants I. BAQUERIZO, V. GALLARDO, A. PARERA, and M. A. RUIZ, Pharmacy and Pharmaceutical Technology Department, School of Pharmacy, University of Granada, E-18071 Granada, Spain. Accepted for publication March 10, 1998. Synopsis Silicone surfactants can be used to prepare emulsions at 15øC, and yield stable w/o and w/s/o emulsions with excellent appearance and optimum hydrating and protective properties. The high water content of the resulting emulsions (about 75%) also makes them economical to produce. We describe the characteristics and advantages of two silicone surfactants, CD Q2-5200 (a laurylmethicone copolyol) and Abil WE 09 (a cetyldimethicone copolyol-polyglyceryl-4-isostearate-hexyl laurate) for use in emulsions. Volatility and freezing point were determined to judge the suitability of these surfactants. Rheological assays were done to determine the most appropriate and stable formulation and form of dispensing. The influence of different concentrations of glycerine, propylene glycol, and polyethylene glycol 400 on these properties was deter- mined at different temperatures. INTRODUCTION The physical properties and usefulness of silicones have been widely studied as the use of these substances has increased. Modifications in chemically complex silicone polymers have been investigated to enhance their solubility in water and other polar solvents, and to improve their affinity for specific biological substrates such as human skin (1). Current research is aimed at developing emulsifying silicone compounds for use in stable water/oil formulations with optimal hydrating and protective properties and good physi- cal appearance. Because of their high water content (approximately 75%), such formu- lations are also economical (2). Modifications in polydimethylsiloxanes (PDMS) and the insertion of alkyl radicals have produced excellent w/o surfactants, which in turn have made it possible to produce w/o or w/s emulsions of varying viscosity, depending on the percentage composition and type of oil phase (3). The advantage of these new surfactants is that they can be used in emulsions containing any of a wide variety of lipophilic components. Stability is not impaired by the com- position of the oil phase, and excellent base substances can thus be obtained for the formulation of different cosmetic emulsions (4). 89