Elastic and quasielastic light-scattering studies of the aggregation phenomena in water solutions of polystyrene particles

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Abstract
We report measurements on the aggregation processes in a colloidal solution of polystyrene particles performed by elastic (intensity) and quasielastic light scattering. In order to observe the different kinetics of aggregation of the system, reversible flocculation, and the slow and the fast irreversible coagulation, the experiment was made varying the concentration of a simple electrolyte (NaCl) in the 0.01–3 mol/liter range. Intensity data give direct information that aggregated clusters are built with fractal structure and different kinetics; in the slow regime the aggregation process is reaction limited, whereas in the raft regime we have a diffusion-limited cluster-cluster aggregation. Dynamical data, showing well-defined scaling behavior in the measured mean linewidth, confirm such a picture and give a rough estimate of the cluster dimension. Experimental results are consistent with the Derjaguin-Landau-Verwey-Overbeek theory on colloidal stability [Derjaguin and Landau, Acta Phys. Chim. Debricina 14, 633 (1941); Verwey and Overbeek, Theory of the Stability of Lyophobic Colloids (Elsevier, Amsterdam, 1948)].