Effect of polymer adsorption on PEO-coated latex particles during salt-induced aggregation

The salt-induced aggregation of polystyrene particles in dilute aqueous solutions has been studied by means of dynamic light scattering measurements and the hydrodynamic radius of the resulting aggregates has been evaluated during the time evolution of the whole process. Poly(ethylene oxide) (PEO) polymer adsorbed on the particle surface at different amounts has been used to modify the inter-particle interactions resulting in the formation of clusters of increasing size or in the stabilization of the suspension, depending on the polymer molecular weight. The aggregation regime, i.e. a diffusion limited cluster aggregation (DLCA) occurring in the polymer-free latex suspension, is partially modified according to the polymer percentage adsorbed on the particle surface. At high polymer content, the polystyrene latex undergoes a complete steric stabilization. The deviation from a DLCA regime has been observed for different polymer contents and for polymers of different molecular weights, from 1.5 to 2000 kD. The alterations of the aggregation rates, induced by the polymer interactions, are presented and briefly discussed.