| Abstract
| - The electrochemical quartz crystal microbalance (EQCM) was used to investigate the sol−gel processfrom an aqueous sodium metasilicate solution at 25 °C and pH 3. From the EQCM data it was possibleto 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 sensorsurface. This additional information was used to estimate, using a model for film formation kinetics, thesol particle size (the model prediction was confirmed by light scattering measurements). The particle sizeestimation was of importance in the analysis of the sol viscosity behavior during the earlier stages of theparticle aggregation process. The analysis, based on a classical model for the viscosity of a dispersion ofcharged particles in an electrolyte, provided some insight into the initial aggregation phenomena andmicrogel formation. Determination of the gelling point was made by examining the evolution of the shearstorage modulus of the system. The gelation point was identified as being the time at which the storagemodulus rose abruptly from zero. The rheological behavior of the system beyond the gelation point wasanalyzed in terms of the loss tangent, which value decreased noticeably before becoming constant. Theobserved decrease in the loss tangent, as a measure of the increasing importance of the elastic energystorage relative to the energy dissipation in the gel, was evidence that Si−O−Si bond formation continuedto take place for some time after the sol−gel transition.
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