AGGREGATION FRAGMENTATION OF COLLOIDAL ALUMINA .1. ROLE OF THE ADSORBED POLYELECTROLYTE

The stability of colloidal alumina in an aqueous suspension containing 10(-3) N KCl, 3 X 10(-4) N AlCl3 and polyacrylic acid was followed ov er 6 weeks. The concentrations of polymer, aluminum ions, and hydrogen ions in solution and the zeta potential of the colloid-polymer comple xes were determined, while the initially predominant aggregation and s ubsequent fragmentation processes were monitored using a particle-coun ter technique. The size frequency curve c(n, t) vs n enabled the weigh t S(t) and number N(t) average sizes of the aggregates to be calculate d and the kinetics of aggregation and fragmentation to be described. T he colloidal stability of the system was found to vary with time and t o be strongly correlated to the polymer dosage, the stability/instabil ity threshold being fixed by the charge characteristics of the interfa cial polymer layer. This experimental system could be appropriate for schematizing some natural systems involving partially soluble oxides a nd polymeric organic materials. (C) 1995 Academic Press, Inc.