Aqueous Sol−Gel Process in the Silica−Metasilicate System. A Microrheological Study

The electrochemical quartz crystal microbalance (EQCM) was used to investigate the sol−gel process from an aqueous sodium metasilicate solution at 25 °C and pH 3. From the EQCM data it was possible to obtain information on the changing rheological properties of the system during the whole process. Besides sensing changes in the rheological properties, the EQCM detected film formation on the sensor surface. This additional information was used to estimate, using a model for film formation kinetics, the sol particle size (the model prediction was confirmed by light scattering measurements). The particle size estimation was of importance in the analysis of the sol viscosity behavior during the earlier stages of the particle aggregation process. The analysis, based on a classical model for the viscosity of a dispersion of charged particles in an electrolyte, provided some insight into the initial aggregation phenomena and microgel formation. Determination of the gelling point was made by examining the evoluti...