STUDIES OF AGGREGATION KINETICS OF POLYSTYRENE LATICES STERICALLY STABILIZED BY POLY(N-ISOPROPYLACRYLAMIDE)

The aggregation of polystyrene latices sterically stabilized by poly(N -isopropylacrylamide) has been studied using dynamic light scattering. The time dependence of the aggregate growth could be monitored under appropriate experimental conditions. The measured fractal dimension wa s found to increase with an increase in the aggregation rate and in th e. salt concentration, as well as the temperature. These unexpected ob servations do not conform to the predictions of the current models for aggregation of electrostatically stabilized particles. It was also in ferred that the restructuring process was different from that reported in the literature. The hydrophobic interaction (or hydration), which is controlled by the salt concentration and temperature, is believed t o play a crucial role in the present system in the aggregation process and in the nature of the aggregate structures formed. The results ind icate that the fractal dimension increases with an increase in the hyd rophobic interaction, i.e., with a decrease in the interparticle inter action energy. This is in good agreement with the predictions of the c omputer simulations of Shih, Aksay, and Kikuchi [Phys. Rev. A 36, 5015 (1987)].