Rheology of the gelation process of silica gel

The rheology of silica sols prepared from mixtures of tetramethoxysilane (TMOS)-methanol-water under basic neutral conditions has been studied at 25, 40 and 60 ° C during the gelation process. The sols show non-Newtonian pseudoplastic behavior from the time of preparation with the appearance of yield stress near the gelation point. The results are analysed using rheological equations of state and the concept of the point of gelation is discussed. For neutral sols an apparent activation energy of 10 Kcal/mol is attributed to the process of polymerization. Qualitative determination of the gelation time for sols prepared under acidic, neutral and basic conditions is also reported at 25° C and as a function of the water content.