Spherical latex particles were used as a colloid model to investigate the aggregation process resulting from the action of electrolytes and polyelectrolytes. The colloid size distribution was directly determined using a particle counter technique. Bell shaped curves were expected for diffusion limited aggregation (DLA) when particle sticking succeeded each interparticle collision. The colloid size frequency was described by a continuously decreasing curve when reaction limited aggregation (RLA) was expected. The last mode implied that the collision efficiency for sticking might depend on the aggregate size. Starting with the cluster size distribution, we calculated the different moments of the size distribution.
When electrostatic forces modulated the interparticle interactions, in the presence of a excess of electrolyte or at a polymer concentration inducing fast aggregation, the reduced size distribution exhibited a typical maximum and the aggregation kinetic was described by a simple scaling law. As a result, a time invariant size polydispersity characterized the long time behavior. Apart from these ideal coagulation conditions, the flocculation proceeded at a slower rate and the dynamic scaling laws required two scaling exponents, w and z. The cluster size polydispersity factor increased with aggregation period as a result of variable collision efficiency.
When flexible polymer acted as an interparticle bridging agent, the amount of polymer adsorbed on a colloid surface also modulated the rate of aggregation but the aggregation mode itself was only determined by the poly- mer/colloid interaction. Fast aggregation wets found to induce maximal cluster size polydispersity.
In all these situations, colloid aggregation modes were analyzed using the results of computer simulation of the cluster-cluster aggregation and the experimental results were presented via a scaling approach. Validity of scaling relations was verified for electrolyte and polyelectrolyte induced aggregation and the different processes corresponded to diffusion and reaction limited aggregatio
