Weak aggregation of charge stabilised dispersions

Abstract

Aggregation equilibria in polystyrene latex and graphitised carbon dispersions have been studied by an automatic particle counter technique. The expected invariance of a simple equilibrium ‘constant’ was not found, the extent of aggregation being (relatively) less at higher particle concentrations and also in the presence of an added non-aggregating dispersion. The concentration effect diminished as the temperature increased. This behaviour is attributed to an energy input (from turbulence necessarily produced by the experimental procedure) leading to collision induced aggregate dissociation. Effective Hamaker functions were obtained after extrapolation of the aggregation behaviour to zero particle concentration and for graphitised carbon the result was consistent with a secondary minimum aggregation model. For polystyrene, however, it is likely that a primary minimum of restricted depth is involved.