抄録
In the past, skincare products have only focused on the function of caring for the skin. In practical use, however, base makeup products such as foundations are applied on dried cosmetic films of skincare products. Generally speaking, in order to obtain a natural finish, the foundations should be applied evenly. Hence, we aimed to develop new formulations of skincare products which have excellent compatibility with makeup foundations. Silicone surfactants provide a lower surface tension than hydrocarbon surfactants. Due to this low surface tension, excellent spreading capacity and skin compatibility are thought to be obtainable. We reported a novel silicone surfactant, 3-(10-carboxydecyl)-1,1,1,3,5,5,5-heptamethyl trisiloxane (CDTS) and found an α-form hydrated crystalline phase (often referred to as “α-gel,” especially in the cosmetics field), composed of CDTS, polyoxyethylen (e 5 mol) glyceryl monostearate (GMS-5), fatty alcohol, and water. In this study, we first investigated the fundamental physical properties of CDTS. The water solubility of CDTS is quite low (ca. 17 μmol/L) and its approximate pKa is 5.7 at 20 ºC. Titration curves also indicated that CDTS is a weak acid. We observed a microemulsion (ME) phase containing CDTS, GMS-5, fatty alcohol, dimethicone, and hydrogenated polydecene. A novel fine nanoemulsion, whose diameter was less than 100 nm, was obtained by the dilution of the microemulsion phase with the water phase. The obtained fine emulsion was applied for tribology tests. Tribological characteristics indicated that the fine emulsion containing the CDTS α-form hydrated crystal is superior to conventional fine emulsions composed of polyoxyethylene 60 mol hydrogenated castor oil, from the viewpoint of low friction at application. Moreover, powder foundation could be applied evenly on the dried cosmetic film of fine emulsions containing CDTS.
