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 TiO
2 and a vinyltriethoxysilane (VTES) system. The hydrophobicity afforded by VTES treatment were determined as a function of parameters such as the VTES/EtOH/Aq.CH
3COOH ratio, pH of aqueous phase, duration of pretreatment with VTES solution, H
2O/VTES ratio and heat treatment temperature of VTES treated product. It was found that the molar ratio of H
2O/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 TiO
2 can be achieved using VTES solution containing a stoichiometric amount of H
2O 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 TiO
2 treated with VTES solution.
3. Heat treatment of TiO
2 powders treated with VTES is essential to provide a hydrophobic property to TiO
2. 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 TiO
2 substrate.
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