Time resolved small angle X-ray scattering of inorganic-organic gel formation kinetics

Formation of hybrid inorganic-organic gels prepared from triethoxysilyl terminated poly(tetramethylene oxide) (ET-PTMO) and tetraethoxysilane (TEOS) by a two-step sol-gel process was investigated using time-resolved small-angle X-ray scattering (SAXS). Reaction conditions used in the first step of the process (high excess of water, acid catalyst) allowed nearly complete hydrolysis of ethoxysilyl groups to silanols. As revealed by SAXS, an excess of base catalyst in the second step promotes formation of primary silica particles and their aggregation in the environment of the swollen polymer network formed simultaneously. The size of the particles and their aggregates sizes were studied as a function of reaction conditions (molar ratios of TEOS/polymer and acid/base catalyst). Higher TEOS content resulted in bigger primary particles initially formed in the second step of the process. The 'fractal' dimension of aggregates was found to be about 2.2-2.4 corresponding to more compact aggregates. (C) 1998 Elsevier Science B.V. All rights reserved.