Rheology Control of Cosmetics Using Aqueous Tickeners

Aqueous thickeners play an important role in both functional and sensory aspects of cosmetic formulas. We report our attempts to use microgels as intelligent aqueous thickeners and quantify the texture of the cosmetic, by using the rheological properties. Agar microgel dispersion prepared from agar bulk-gel was then granulated by a high-speed mixer (5000 rpm). Another microgel was created with an inverse microemulsion polymerization system. The thickening effect of the microgel prepared by using this system was higher than that of the agar microgel. The flow characteristic parameters of the microgels were analyzed by using the Herschel-Bulkley equation. The power index n in the H-B eq. revealed that both the microgels were expected to give a refreshing-feeling. Flow properties of cosmetic lotions, containing various kinds of aqueous thickeners, were studied by creep measurement, and parameters were calculated from their rheological data based on the empirical Nutting equation. There was some correlation between the time dependency parameter a and some sensory evaluation points, as assessed by human panels. Simple linear regression analysis revealed that the evaluation scores of slimy-feeling, sticky-feeling, refreshing-feeling, and penetrating-feeling cosmetic lotions could be reduced to numerical data by the parameter a. This quantification method for the texture of cosmetic products will be a useful tool for efficient development of cosmetic formulas.