Kinetics of salt-induced aggregation in polystyrene lattices studied by quasielastic light scattering

We investigate the kinetics of aggregation of polystyrene particles of 481 nm in a solution of a univalent-univalent salt in the concentration range from 0.05 to 2.6 mol/l. Using quasielastic light scattering to measure the linewidth and hence the hydrodynamic radius of the clusters, we find the value 1.75±{}0.03 for the fractal dimension of the aggregates in the fast coagulation regime, when the salt content is high, while we get a slow exponential kinetics with low salt content. Using scaling arguments and the mean-field Smoluchowski equation we describe our results in terms of collisions of clusters during purely Brownian diffusion.