Coupling Treatment of TiO2 Powders with Vinyltriethoxysilane

To obtain fundamental findings on providing an inorganic substrate with hydrophobic properties using a silane coupling agent by the dry method, which is often limited by an uneven product, a fundamental study was performed using TiO2 and a vinyltriethoxysilane (VTES) system. The hydrophobicity afforded by VTES treatment were determined as a function of parameters such as the VTES/EtOH/Aq.CH3COOH ratio, pH of aqueous phase, duration of pretreatment with VTES solution, H2O/VTES ratio and heat treatment temperature of VTES treated product. It was found that the molar ratio of H2O/VTES, pH of aqueous phase, pretreatment duration of VTES solution, and heat treatment temperature are important parameter to determine coupling effect.The principal findings obtained are as follows.1. Optimum treatment of TiO2 can be achieved using VTES solution containing a stoichiometric amount of H2O at aqueous phase pH 3.3 after storing for more than 36hrs.2. The pH value in the aqueous phase is intimately related to hydrolysis and condensation reactions of VTES, and thus to the hydrophobic properties of TiO2 treated with VTES solution.3. Heat treatment of TiO2 powders treated with VTES is essential to provide a hydrophobic property to TiO2. However an excessively high temperature causes evaporation of hydrolysis and condensation products of VTES, resulting in poor hydrophobicity.4. The required amount of VTES can be calculated by applying a closed packing model of VTES to the TiO2 substrate.