TIME-RESOLVED SMALL-ANGLE X-RAY-SCATTERING OF INORGANIC-ORGANIC GEL FORMATION KINETICS

Formation of hybrid inorganic-organic gels prepared from triethoxysily l terminated poly(tetramethylene oxide) (ET-PTMO) and tetraethoxysilan e (TEOS) by a two-step sol-gel process was investigated using time-res olved small-angle X-ray scattering (SAXS). Reaction conditions used in the first step of the process (high excess of water, acid catalyst) a llowed nearly complete hydrolysis of ethoxysilyl groups to silanols. A s revealed by SAXS, an excess of base catalyst in the second step prom otes formation of primary silica particles and their aggregation in th e environment of the swollen polymer network formed simultaneously. Th e size of the particles and their aggregates sizes were studied as a f unction of reaction conditions (molar ratios of TEOS/polymer and acid/ base catalyst). Higher TEOS content resulted in bigger primary particl es initially formed in the second step of the process. The 'fractal' d imension of aggregates was found to be about 2.2-2.4 corresponding to more compact aggregates. (C) 1998 Elsevier Science B.V. All rights res erved.