The dynamics and structure have been compared for two types of silica gels prepared from tetramethoxysilane in dimethylformamide under acidic and basic conditions. An in-situ time-resolved dynamic light scattering (TRDLS) technique was employed to investigate the changes of the dynamics during gelation process. In both cases, a clear power-law behavior in the time-intensity correlation function, g((2))(tau) -1 similar to tau(n-1), was observed at the gelation threshold, from which the critical exponent of viscoelasticity, n, was evaluated. The gelation of the acid system was slower, and the gelation time was a weak decreasing function of the initial monomer concentration, C. The resultant gel was found to be made of long polysiloxane chains slightly connected with each other, which was characterized by n approximate to 0.5. On the other hand, the gelation time of silica gels prepared with a basic catalyst was strongly dependent on C. The evaluated value n approximate to 0.73 indicates the presence of highly branched clusters with short strands. It is demonstrated that the TRDLS technique is a powerful tool to investigate gelation process of silica from both dynamic and structural points of view.
