Water-repellent coating films on glass prepared from hydrolysis and polycondensation reactions of fluoroalkyltrialkoxylsilane

Abstract

Water-repellent glasses for automotive windows are new glass products in which several kinds of fluoroalkylsilanes are used to modify the surface properties of the glass substrates. We examined the hydrolysis and polycondensation reactions of a fluoroalkyltrimethoxysilane (FAS), CF 3(CF 2) 7CH 2CH 2Si(OCH 3) 3, by using gas chromatography, gel permeation chromatography and time-of-flight mass spectroscopy. Dimers, trimers and higher polymerized species of FAS were formed by dehydrating the water-repellent coating solutions after a hydrolysis process. The polymerized species of FAS are preferable for improvement of the durability of the water-repellent glasses. However, the excess polycondensation of FAS deteriorates the abrasion resistance, because of the decrease in the number of silanol groups, which are bound to the glass surface. Therefore, appropriate amounts of the polymerized species of FAS play an important role in improving both the abrasion resistance and the UV-light resistance of the water-repellent glasses. The water-repellent glasses obtained from the dehydrated water-repellent coating solution thus show higher durability than those obtained from the non-dehydrated one.