AGGREGATION DISPERSION OF AMORPHOUS SILICA PARTICLES BY SIMULTANEOUS ADSORPTION OF 2 POLYMERS IN AN AQUEOUS PHASE

The effect of simultaneous adsorption of two polymers on the mean diameter, d, of secondary particles of amorphous silica (Micon FN) was studied. The d value was decreased by the adsorption of sodium chondroitin-6-sulfate (Na2Chs) or sodium carboxymethylcellulose (NaCMC), although the amount of Na2Chs or NaCMC adsorbed was lower than that of polyvinylpyrrolidone (PVP), a flocculating agent. The amount of adsorbed Na2Chs or NaCMC decreased in the presence of PVP due to competitive adsorption, but that of PVP increased, due to the disintegration of silica aggregates caused by the adsorption of Na2Chs or NaCMC. The zeta potential of Micon FN became less negative on adsorption of PVP, due to the protrusion of the polymer loop, but became more negative by the adsorption of Na2Chs or NaCMC in either the presence or absence of PVP, indicating that electrostatic repulsion is important for the dispersion of silica particles. In the case of PVP, non-electrostatic effects such as steric hindrance and interparticle bridging are dominant factors for the dispersion and flocculation.