FORMATION AND STRUCTURE OF POLYSTYRENE LATEX AGGREGATES OBTAINED BY FLOCCULATION WITH CATIONIC POLYELECTROLYTES .1. ADSORPTION AND OPTIMUM FLOCCULATION CONCENTRATIONS

The adsorption of modified polyacrylamide polyelectrolytes and their effect on the flocculation of negatively charged polystyrene latex were investigated. Conditions were chosen so that the adsorbed polymers approached equilibrium configuration before the occurrence of appreciable flocculation. Polymers with very low charge density (a few percent charged monomers) form loops and tails at the latex surface and flocculate the latex by bridging. Polymers with higher charge adsorb in a flat configuration and flocculate the latex by net charge neutralization, possibly leading to long-range attraction between positively and negatively charged domains on different particles. Minima in the ratio of the total polymer charge adsorbed at the plateau level to the total charge on the latex occur at intermediate polymer-charge densities. At these densities the mean distance between charged groups on the polymers matches the mean distance between charged groups on the latex. At maximum adsorption of highly charged polymers, the latex particles acquire a high positive charge. The reason for this is that the mean distance between positive charges on the polymer is smaller than the distance between charges on the latex, so that ion binding of the polymer to the ionized latex surface groups cannot take place without simultaneous attachment of an excess of positive charge to the latex surface.