Rheological analysis of the gelation behavior of tetraethylorthosilane/vinyltriethoxysilane hybrid solutions

Abstract

The gelation behavior of tetraethylorthosilane (TEOS) sol in the presence of a silane coupling agent vinyltriethoxysilane (VTES) was investigated experimentally. Specifically, the gel time and gel structure were analyzed by the theological multiwave test of Fourier transform mechanical spectroscopy (FTMS) for the mixtures of TEOS/VTES with various molar ratios at different temperatures. Gelation was accomplished through the sol-gel reactions of the silicon alkoxide TEOS in aqueous acidic solution. The results showed that, at elevated temperatures, the gel point was scattered and obscured by the noise in low frequencies owing to the enhanced thermal agitations. In this case, the statistical method was used to find the exact gel time. The activation energy of gelation and the gel exponent ranged from 25 to 30 kJ/mol and from 0.581 to 0.771, respectively, depending on the TEOS/VTES composition. The fractal dimension was estimated from the gel exponent and indicated the gel structure and that the TEOS/VTES solutions formed a relatively open and coarse gel structure.