Viscosity stability of O/W emulsion containing α-gel through an ionic-complex system

Although many active ingredients are used in cosmetic products for moisturizing and whitening the skin, they are often electrolytes, and the stabilities of oil in water (O/W) type emulsion formulae containing electrolytes are generally difficult to control. To solve this problem, formulae containing an α-crystalline phase (α-gel) consisting of water, higher alcohols, and anionic surfactants such as sodium N-stearoyl-N-methyl-taurate (SMT) have been developed. However, in spite of their excellent salt tolerance, these formulae have poor viscosity stability under non-electrolyte conditions, and the viscosity decreases over time. To obtain adequate viscosity stability, the required electrolyte concentration is approximately 1wt%, which is somewhat high for cosmetic applications. To replace the salts, distearyl dimethyl ammonium chloride (DSAC), a cationic surfactant, with an opposite electric charge to SMT, was used in O/W emulsion formulae, resulting in improved viscosity stability at a lower concentration than that of salts. The stabilization mechanism with DSAC was found to be different from that of salts.