Colloid aggregation in the presence of polymers. Effects of mobility and reactivity of clusters on the flocculation kinetics

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Abstract
Small spherical lattices were used to model submicronic particles in a study of polyelectrolyte induced aggregation of colloids. The colloid concentration of the suspension was investigated with a particle counter, allowing determination of the aggregate size distribution and calculation of the average colloidcharacteristics. Dynamic scaling describes the aggregation kinetics: the number and the weight average sizes scale with flocculation time. The temporal variation of these characteristics is interpreted in the light of simulation results, for which the influence of the cluster mobility and cluster reactivity has been independently determined. Information relative to the variation of the aggregate compactness with the aggregate size is obtained from experimental and simulation studies. When colloid–polymer complexes aggregate by forming interparticulate polymer bridges, aggregation is generally found to develop with features of the reaction limited aggregation process. In the present case, this mode was disturbed by the unusual size dependent colloid mobility. Aggregates of small size were characterized by a relatively low mobility due to their loose structure. Aggregates of large size, which emerged during the terminal step of aggregation, displayed a relatively high mobility as a result of their increased compactness. We determined that, during flocculation, the process started with characteristics of diffusion limited aggregation and ended up with features of the reaction limited process. The transitory mode showed that aggregation developed in accordance with the assumption that aggregates of different sizes might have closely related mobilities.