Small-angle X-ray scattering from wet gels prepared from co-hydrolysis of tetraethoxysilane and vinyltriethoxysilane

Abstract

Small-angle X-ray scattering was used to study the structure of wet gels prepared from co-hydrolysis of tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) in the VTES/(VTES + TEOS) molar ratio ranging from 0 to 1. The wet gels at pH = 6 behave as a mass-fractal structure with characteristic size ξ and fractal dimension D, both increasing with the amount of VTES from ξ = 6.78 nm and D = 2.25 for pure TEOS until an almost homogenous structure with ξ ~ 24.9 nm and D ~ 2.85 is obtained for the wet gel prepared with pure VTES. The mass-fractal structures are built up by small primary clusters of characteristic size between ~0.35 and ~0.85 nm, the size increasing with the quantity of VTES. These small particles of the gels are formed by a restructuring process of a few larger macromolecules in the stable sols (pH = 2) on passing from the acid to the increased-pH step of the process.