SAXS study of gelation, aging and drying of silica-polypropyleneglycol hybrid materials

New silica-polypropyleneglycol ormosils (organically modified silicates) wi th covalent bends between the organic (polymer) and inorganic (silica) phas es have been prepared by the sol-gel process. Their structural evolution du ring sol formation, sol-gel transition, gel aging and drying has been studi ed in situ by small-angle X-ray scattering (SAXS). The experimental SAXS cu rves corresponding to sols and gels exhibit features expected from fractal objects. Clusters of size around 55 Angstrom with an initial fractal dimens ion D = 2.4 are formed in the sol. They are constituted of small primary si lica particles chemically crosslinked at the end of the polymer chains. A s trong liquid-like spatial correlation between the silica particles develops during drying due to the shrinkage of the polymeric network induced by wat er and ethanol evaporation. The continuous increase in SAXS intensity durin g drying, while the interparticle distance remains constant, is a consequen ce of the progressive growth of the dry fraction of the total volume. After drying, the gel structure consists of a rather compact arrangement of sili ca particles embedded in the polypropyleneglycol matrix.