Metal Oxide Particle Dispersion Controlled by Volatility and Affinity of Oil Medium and Its Application to Cosmetics

Abstract

Titanium dioxide and zinc oxide particles have been used in sunscreens as UV filters. Generally, these nanoparticles are formulated as dispersions with an oil medium. Flocculation of the particles has been regarded as “taboo” in the formulations of sunscreens because it results in the reduction of the UV protection efficiency and the problem of an unnatural white cast of the skin. In this study, we developed a new dispersion composition of the mineral UV filters as well as discovered a dynamic structural change of the flocculation system. An applied film of the newly developed dispersion exhibited a dramatic optical transition with a dynamic de-flocculation of the particles, where the UV protection efficiency and the visual transparency were enhanced over the drying time of the film. This was triggered by the evaporation of a poor solvent and the recovery of the solvent affinity to the dispersant. In addition, the original flocculation of the dispersion suppresses the spontaneous flow of the applied liquid into the skin furrows and pores, which leads to the formation of a uniform film on the skin. As a result, the new dispersion system had excellent UV protection performance compared to a system with originally well-dispersed UV filters.

graphical abstract