Studies of aggregation kinetics of polystyrene latices sterically stabilized by poly(N-isopropylacrylamide)

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Abstract
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 was found to increase with an increase in the aggregation rate and in the salt concentration, as well as the temperature. These unexpected observations do not conform to the predictions of the current models for aggregation of electrostatically stabilized particles. It was also inferred 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 to play a crucial role in the present system in the aggregation process and in the nature of the aggregate structures formed. The results indicate that the fractal dimension increases with an increase in the hydrophobic interaction, i.e., with a decrease in the interparticle interaction energy. This is in good agreement with the predictions of the computer simulations of Shih, Aksay, and Kikuchi [Phys. Rev. A 36, 5015 (1987)].