Authors: A.S. Moussa, L. Ehrl, M. Soos, M. Lattuada, M. Morbidelli
Affilation: ETH Zürich, Switzerland
Pages: 681 - 684
Keywords: aggregation, coagulation, flocculation, DLVO theory, colloidal interactions, colloidal dispersions, breakage mechanism, light scattering, surface chemistry, hydration repulsion, hydrophobic attraction, aggregate strength
Static light scattering was used on-line 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, different surface densities of charge groups, and different hardness were investigated. For each latex, a series of aggregation experiments at various pH values was carried out. For all experiments the solid volume fraction, the rotation speed and the salt concentration -above the critical coagulation concentration- were the same. Three remarkable observations were made: first, average aggregate size increased with decrease in pH for both latexes and full grown aggregates were still responsive to the pH. Second, qualitatively different behaviors of the temporal evolution of moments of the cluster mass distribution were observed below certain pH values. Third, the average sizes of the 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. Different hypotheses were postulated and tested to explain the observations. From the experiment we concluded that structural forces and contact hysteresis can play an important role in flow-induced aggregation and breakage.