Hideo Nakajima

Preparation and Thermal Properties of Fatty Alcohol/Surfactant/Oil/Water Nanoemulsions and Their Cosmetic Applications

Physicochemical properties of oil-in-water (O/W) emulsions containing fatty alcohols and surfactants have been investigated with the aim of developing new formulations that are less viscous and more transparent than conventional milky lotions, as well as for providing greater skin-improving effects. O/W-based creams can be converted to low viscosity milky lotions following their emulsification with a homogenizer at temperatures greater than the transition temperatures of their molecular assemblies (α-gel). The stability of the O/W emulsions evaluated in the current study increased as the transition temperatures of the molecular assemblies formed from their fatty alcohol and surfactant constituents increased. A decrease in the emulsion droplet size led to the formation of a new formulation, which was transparent in appearance and showed a very low viscosity. The absence of a molecular assembly (α-gel) formed by the fatty alcohol and surfactant molecules in the aqueous phase allowed for the formation of a stable transparent and low viscosity nanoemulsion. Furthermore, this decrease in droplet size led to an increase in the interfacial area of the emulsion droplets, with almost all of the fatty alcohol and surfactant molecules being adsorbed on the surfaces of the emulsion droplets. This was found to be important for preparing a stable transparent formulation. Notably, this new formulation exhibited high occlusivity, which was equivalent to that of an ordinary cosmetic milky lotion, and consequently provided high skin hydration. The nanoemulsion was destroyed following its application to the skin, which led to the release of the fatty alcohol and surfactant molecules from the surface of the nanoemulsion into the aqueous phase. These results therefore suggest that the fatty alcohol and surfactant molecules organized the molecular assembly (α-gel) and allowed for the reconstruction of the network structure.

Characterization of Ethyl Cellulose as W/O-Type Emulsifier and Application for Sunscreen

化粧品において皮膜剤として用いられてきたエチルセルロースについて, その両親媒性構造に着目し, 乳化剤としての可能性を検討した。種々の油分を用いて乳化を試みた結果, エチルセルロースが極性油をW/O乳化可能であることが見出された。蛍光ラベル化したエチルセルロースを用いた評価系の結果から, エチルセルロースは界面に吸着層を形成すると同時に連続相に構造体を形成することで, W/O型エマルションを安定化することが示唆された。このエチルセルロースを用いたW/O型エマルションは, イソステアリン酸とカルボキシメチルセルロースNaの添加によりさらに安定化し, 化粧品として要求されるレベルまで安定化できることがわかった。本基剤の特長は, 従来乳化が困難であった極性油を安定にW/O乳化できる点にあるため, サンスクリーン剤への応用を次に試みた。この結果, エチルセルロースは乳化剤として作用し, エマルションが調製されると同時に, 塗布後は皮膜剤として作用し, 高い耐水性を与えることが示された。