Correlation between the formation of silica skeleton structure and Fourier transform reflection infrared absorption spectroscopy spectra

A Fourier transform reflection infrared absorption spectroscopy (FT-IRAS) technique was applied to filmy silicas prepared from sols with various viscosities synthesised by the hydrolysis of tetraethoxysilane (TEOS). Two characteristic infrared (IR) absorption peaks were observed at 1225 (longitudinal mode) and 1065 cm(-1) (transverse mode) for the film prepared from the sol at 3 mPa s viscosity. The wave number and the band intensity of each mode in the absorption peaks depend on the viscosity of the sol used in the film preparation and the dependency of each mode notably observed in the oligomer formation viscosities (approximate to 7-12 mPa s). The band intensity change for such oligomers was fitted to the resultant dipole moment with the planar ring structure calculated from the -[Si-delta (+) -Odelta- (Si)](n)- chain. It may be that the structure of a starting oligomer formed in the early stage of condensation is that of planar 3- or 4-hold ring. (C) 1999 Elsevier Science B.V. All rights reserved.