Preparation of water powders by the adsorption of hydrophobic nanoparticles at the surface of hydrated starch particulates

Water powders, aqueous droplets stabilized by the adsorption of hydrophobic nanoparticles at surface, were prepared for the cosmetic applications. The mild shear stress applied to water powders can induce the collapse of powders, and release water to skin. The hydrophobicity of nanoparticles, measured by the contact angle with water, played an important role for the formation of water powders. When the contact angle of nanoparticles with water was between 126 and 138°, the stable water powders were formed. The surfaces of silica or TiO2 nanoparticles were modified with dimethicone or alumina to control the hydrophobicity of nanoparticles. Also the size of nanoparticles was one of the key factors in forming water powders. When the size of nanoparticles was 1/500–1/750 compared with that of modified starch particulate, the water powders were formed well. The modified starch particulates were swelled with aqueous phase. The optimal amount of aqueous phase in water powder was 75–80% by weight. Even though the content of aqueous phase was very high, the appearance of water powder was powdery. The water powders prepared at various conditions were investigated with SEM and an optical microscope.