Branching, aggregation, and phase separation during the gelation of tetraethoxysilane

Time-resolved small-angle X-ray scattering is used to follow in situ the structuring of silica sols and gels in various chemical conditions. The acid-catalyzed and base-catalyzed polymerizations of TEOS, as well as the copolymerization of TEOS with organically modified trialkoxysilanes, are followed. The analysis points to the diversity of the mechanisms that govern the structuring of the reacting solutions, and most notably to the important role of physical forces.