COUPLING BETWEEN POLYMER ADSORPTION AND COLLOIDAL PARTICLE AGGREGATION

Studies of the adsorption of high molecular weight polymers on colloid al latex and silica particles and their subsequent flocculation were c arried out. Neutral polyethylene oxide samples with both a narrow and a broad molecular weight distribution were used together with low char ged cationic copolymers. The influence of the particle concentration a nd polymer dose on the flocculation were systematically investigated u nder quiescent conditions. Equilibrium bridging only occurred with pol yelectrolyte, even in very dilute suspensions, at high particle covera ge. In contrast to this, non-equilibrium bridging occurred with both n eutral polymer and polyelectrolytes but only for more concentrated sus pensions and small amounts of adsorbed polymer. Polymer adsorption in dilute suspensions, which did not show particle aggregation was measur ed an electrophoretic technique. In more concentrated suspensions, whe re flocculation takes place, we found that aggregation prevents furthe r polymer adsorption and induces both an excluded volume and a surface effect. The consequences on the shape of the isotherms differ accordi ng to the aggregation mechanism. A significant decrease of the amount, Tau, of adsorbed polymer is observed with non-equilibrium bridging. W hen both mechanisms simultaneously contribute to the aggregation, the value of Tau depends on their relative importance. In the intermediate range of copolymer dose their respective contributions are critically sensitive to the details of the mixing step and stirring, leading to non reproducible experimental results.