SMALL-ANGLE X-RAY-SCATTERING STUDY ON SOL-GEL TRANSITION OF MIXTURES OF COLLOIDAL SILICA AND ORGANIC POLYMER

Sol-gel transition of mixtures of colloidal silica-water soluble organic polymer (sodium polystyrenesulfonate) has been investigated by the small-angle X-ray scattering technique. With proceeding gelation, an increase of the intensity at small-angle regions was observed and the values of radius of gyration (R(g)) were estimated by the Guinier method. The addition of polymer increased the initial increase of R(g) with gelation, i.e., sol-gel transition was accelerated by the presence of the polymer. This observation is not in contradiction to the prediction of micro-phase separation into silica-rich phase and polymer-rich phase proposed by Nakanishi and Soga. The fractal analyses predicted that the geometrical structure of the gel finally formed is similar to those of random coil linear polymer and swollen branched polymer.