Perikinetic Aggregation Induced by Chromium Hydrolytic Polymer and Sol.

We investigated the kinetics of destabilization of polystyrene latex particles bearing sulfate surface groups in the presence of aged chromium polymer and oxide sol particles of relatively smaller size employing a particle counting technique. From the mass distribution curve, we derived the weight S(t) and number N(t) average masses of the aggregates. From the variation with time of these characteristics we determined the scaling exponents z and w of the kinetic laws which serve to characterize the aggregation mechanism induced by the inorganic polymer and sol. From the slope of the self-preserved reduced mass distribution, we determined the exponent tau, and found the relationship tau = 2 - (w/z) to be valid. The usual value of tau = 1.5 was obtained for experiments performed in the presence of very small amount of polymer. Deviation from this behavior was determined in the presence of increasing amounts of polymer and sol. At short and long terms, we determined tau to be equal to 1.24 and 1.37, respectively. This was attributed to the diffusion-limited aggregation accompanying the prevailing reaction-limited process, which was found to provide an unusual mass distribution frequency characterized by a hump in the monotonically decreasing curve. From the comparison between the aggregation rates and the apparent aggregate reactivity at short and long terms, we concluded that (i) the short-term aggregation involving aggregates of high apparent reactivity is highly reversible and (ii) the long-term aggregation involving aggregates of lower apparent reactivity is irreversible (or less reversible). Copyright 1998 Academic Press.