Development of Unique Technology Using Plasma on a Liquid Surface, and Its Application to Novel Cosmetic Materials

Abstract

Titanium dioxide (TiO2) nanoparticles have been used as ultraviolet light scattering agents in sunscreen cosmetics. However, they tend to self-aggregate due to their high surface energies and strong interparticle attraction in water. In this research, we focused on liquid surface plasma (LSP), and studied the water dispersion technology of fine-particle TiO2. The plasma formed is considered to generate shock waves and species such as O radicals, which have high oxidation potential, around the liquid surface. The LSP treatment enabled preparation of the aqueous dispersions with 10% (wt) TiO2 nanoparticles that have approximately 100 nm particle size and long-term stability. In addition, from the chemical analyses of the dispersions, Al compounds derived from the underwater Al electrode were formed on the TiO2 surface. It was clear that TiO2 nanoparticles had high positive charge under pH neutral condition due to Al compounds on the surface, so that the dispersions were stabilized by electrostatic repulsion between the particles. Furthermore, from the X-ray absorption fine structure (XAFS) measurements, it was found that the chemical state and molecular structure of Ti were not altered by the LSP treatment, and amorphous aluminum hydroxide (Al(OH)3) was detected on the surface. These findings suggest that the TiO2 aqueous dispersion obtained by the LSP treatment can be safely applied to cosmetics. Finally, a composite powder (PLD-TiB), which is BaSO4 covered with TiO2, was obtained by electrostatic combination in aqueous dispersion. From the SEM image, it was observed that the BaSO4 surface was uniformly coated with TiO2. Due to the uniform coating without aggregation, PLD-TiB had a great UV protecting effect and a smooth feeling on the skin.