The Optical Properties of Nanoparticle Dispersions Prepared by a High Speed Thin Film Mixer

Abstract

Ultrafine particles having diameters in the submicron region have often been used as cosmetic materials because they have excellent optical properties, such as transparency and UV light protection. However, these particles have interfacial energy higher than conventional pigments; thus, they have a tendency to interact with each other to form a secondary agglomeration which may cause deterioration of those functions. To solve these problems, applying high shear force using a high-speed mixer is one of the prospective methods to produce monodispersed uniform dispersion of ultrafine particles. In this study, the relationship between optical properties and high-speed mixing was examined using a high speed thin film mixer. When hydrophilic TiO₂ nanoparticles were dispersed in ion-exchanged water, the extinction coefficient decreased in accordance with the peripheral speed of the rotor. Particle size distribution depends on the mixing speed and has good correlation with the increase of distinction coefficient.