Study on the Optically Variable Property of Nano-TiO₂

The morphology and particle size of nano-TiO₂ were analyzed by transmission electron microscopy(TEM),and the optically variable property of the automobile paint made of the nano-TiO₂ was also analyzed by a five-angle colorimeter.The results show that the paint film containing single nano-TiO₂ has no angle-dependent optical effect,showing white phase on the white substrate while blue phase on the black substrate.The automobile paint composed of nano-TiO₂ and aluminum powder has an optically variable property.The particle size of TiO₂ has a great influence on the optically variable property of the paint,where the aluminum paint modified by ordinary titanium white with an average particle size of 280 nm has no angle-dependent optical effect but it shows significant angle-dependent optical effect for the aluminum paint modified the nano-TiO₂ with an average particle size of 35 nm.Furthermore,the color variation from different angles for the paint increases with increase of the nano-TiO₂ addition.The angle-dependent optical effect is originated from Rayleigh scattering occurring on the surface of nano-TiO₂ under illumination,exhibiting a golden yellow phase in the parallel direction with the incident light,blue phase perpendicular to the incident light and blue phase with different degrees in other directions dependent on the angles.