Kinetics of heterocoagulation. Part 4.—Evaluation of absolute coagulation rate constants using a classical light scattering technique
The rate of coagulation in systems of identical and unlike colloids in aqueous media has been studied by a simultaneous multi-angle static light scattering technique. The mixed dispersions consisted of polystyrene latex particles of different radii and of opposite sign of charge. A procedure based on the Rayleigh–Gans–Debye approximation permits one to estimate the absolute rate constant either for homo- or hetero-coagulation. The absolute coagulation rate constants were compared to those calculated theoretically, using the Smoluchowski theory. In homosystems, the fast coagulation rate corresponded to ca. 55–60% of the Smoluchowski value. In the heterosystem, the coagulation rates exceeded the calculated values based on the diffusion-controlled process at a low ionic strength. An increase in the electrolyte content led to a decrease of the coagulation rate, which at high concentrations corresponded to ca. 85% of the Smoluchowski value.