KINETICS OF REACTION-LIMITED CLUSTER AGGREGATION STUDIED BY ELECTRIC LIGHT-SCATTERING

Earlier experimental results from an electric light scattering study o f the slow coagulation of monodisperse spherical alpha-Fe2O3 particles in the presence of a bivalent electrolyte (MgSO4) are discussed on th e basis of fractal growth theory. A more realistic fractal model for t he structure of aggregates is introduced. The kinetics of the changes of three different types of average relaxation time (related to averag e characteristic sizes) are monitored. The experimental results indica te a reaction-limited cluster aggregation process, i.e. slow coagulati on. The slopes of the semilogarithmic dependences of the different typ es of average relaxation time on the aggregation time are approximatel y equal owing to the self-similarity of the aggregates. At the highest electrolyte concentration used, a process of cross-over to fast coagu lation is observed. In this regime, the measured fractal dimension D o f about 1.6 +/- 0.3 is in a good agreement with that of the diffusion- limited cluster aggregation models.