Temporal evolution of the cluster size distribution during brownian coagulation

Abstract

We used an optical pulse particle size analyzer to determine the detailed form of cluster size distributions arising from salt-induced aggregation of polystyrene microspheres. We found that von Smoluchowski theory describes both the shape and temporal evolution of the distribution at short times. This theory assumes that aggregation is unidirectional and irreversible and that the two-particle association coefficient is a constant independent of the size of the interacting clusters. However, we observed a sharp departure from von Smoluchowski theory after roughly three reaction half-lives. This departure may result from the approach to equilibrium and the associated growth of a gel phase. These experiments provide a direct means of testing both the equilibrium and kinetic theories of cluster formation and of probing the two-particle potential, particularly its strength at short range.