Kinetics of reaction-limited cluster aggregation studied by electric light scattering

Abstract

Earlier experimental results from an electric light scattering study of the slow coagulation of monodisperse spherical α-Fe 2O 3 particles in the presence of a bivalent electrolyte (MgSO 4) are discussed on the basis of fractal growth theory. A more realistic fractal model for the structure of aggregates is introduced. The kinetics of the changes of three different types of average relaxation time (related to average characteristic sizes) are monitored. The experimental results indicate a reaction-limited cluster aggregation process, i.e. slow coagulation. The slopes of the semilogarithmic dependences of the different types of average relaxation time on the aggregation time are approximately equal owing to the self-similarity of the aggregates. At the highest electrolyte concentration used, a process of cross-over to fast coagulation is observed. In this regime, the measured fractal dimension D of about 1.6 ± 0.3 is in a good agreement with that of the diffusion-limited cluster aggregation models.