Viscoelastic characterization of three different sol-gel derived silica gels

Three different sol-gel derived silica gels having different gelation mechanism derived both from the acidic and basic sols were investigated. The aggregation processes are monitored by rheological measurements and the viscoelastic behaviour near the gel point is used to determine the critical scaling exponents for each case using frequency dependence of the loss and storage moduli (G″ and G′). The scaling exponents are further analysed in order to obtain information about particle-particle/aggregate interactions in the system. The three aggregation processes forming gels are suggested to fit to the known aggregation theories for the sol-gel transition. The analysed data including estimated fractal dimensions provide information about the gelation process with respect to aggregation. The mechanisms of aggregation have an influence on the gel structure and the data obtained give an insight about the structure formation from a sol to a gel. The dried gels are additionally characterized by atomic force microscopy (AFM).