Surface Treatment of Ultrafine TiO2 Particles by Vapor-Phase Hydrolysis

Ultrafine particles of amorphous TiO2 stabilized by alkylalkoxysilane (AAS) were synthesized by vapor-phase hydrolysis of titanium tetraisopropoxide (TTIP), followed by coating with AAS in the same reactor. The surface of the TiO2 particles produced became hydrophobic. The dispersion of the particles was improved. The dispersion was evaluated by measurement of aggregate size and visible light transmittance in organic solvents. An effective way of decreasing the aggregate size of the particles dispersed in ethanol was to employ highly excessive ratios of water to TTIP. In the case of a hydrophobic solvent like toluene, the aggregate size of particles treated with AAS having more alkoxy groups was very greatly decreased. 29Si-NMR measurement of the surface of the particles showed that the degree of hydrophobicity was correlated with the dispersion of the particles.