(162e) Effect of pH on Flow-Induced Aggregation of Fully-Destabilized Polystyrene Latex

Abstract: Small angle static light scattering (SASLS) was used to monitor the flow induced aggregation of surfactant-free polystyrene latexes in a stirred tank. Various latexes with primary particles diameters ranging between 100 and 300 nm, different charge groups and different surface density of charge groups were investigated. For each latex, a series of aggregation experiments at various pH values was carried out. All experiments were done under the same solid volume fraction, volume average shear rate and salt concentration. Salt concentration was higher than the critical coagulation concentration in all experiments. Three remarkable observations were made: first, average aggregate size increased with decrease in pH for both latexes. Second, qualitatively different behaviors of the temporal evolution of moments of the cluster mass distribution (CMD) were observed below certain pH value. Third, the average sizes of aggregates attained in the experiments using the latex with the larger primary particle are larger than those attained in the experiments using the latex with the smaller primary particles. To elucidate the phenomena behind these observations, we studied experimentally the reversibility of the CMD with respect to the pH, and the effects of stirring speed and initial solid volume fraction on the CMD. In this contribution we report details of the experiments and outline some possible interpretations of the findings.