Plate–sphere hybrid dispersions: Heterocoagulation kinetics and DLVO evaluation

We have studied the formation of colloidal composite particles through the controlled heterocoagulation of anionically charged polystyrene (PS) and poly(isobutyl methacrylate) (PiBMA) latex spheres with positively charged gibbsite platelets. The latex particles, synthesized by emulsion polymerization, varied in size and surface charge density. The heterocoagulation was studied as a function of the number ratio between small latex particles and large gibbsite platelets (NS/NP), ionic strength and pH of the aqueous medium. The coagulation kinetics of latex spheres with inorganic platelets in aqueous dispersions were determined by time resolved dynamic light scattering (TR-DLS) experiments. The NS/NP values should be sufficiently high to prevent the formation of multilayer aggregates. It was shown that the heterocoagulated colloidal particles were stable up to an ionic strength of 2.5 mM for latex particles with a diameter of about 80 nm and ∼30 mM for those of 35 nm, respectively. The effect of pH on the colloidal dispersions was verified by the classical DLVO theory.