RELAXATION PHENOMENA IN SOL-GEL TRANSITION

We performed a large set of quasi-elastic dynamic light scattering mea surements of silica gels (tetramethoxysilicon) catalysed with NH3OH. H omodyne correlation functions were obtained during both slow and fast aggregation processes. In order to interpret our data we use a recentl y proposed model for relaxation in disordered systems, which selects t wo typical time scales in the process of approach to gelation. These t imes separate three different temporal regimes of exponential, power-l aw and stretched exponential decay. Our analysis allows a good descrip tion of the scaling regime associated with the decay and good values f or the corresponding critical indices of the relevant quantities and t he characteristic times close to gelation. (C) 1998 Elsevier Science B .V. All rights reserved.