Adsorption and stability of colloidal silica

In order to describe the influence of cationic polyelectrolytes (PE) on the stability and flocculation of dispersed particles, the polymer adsorption on particles of colloidal silica and quartz powder Sikron was investigated. Poly-methacryloyloxyethyltrimethyl-ammoniumchloride (PM) and poly-methacryloyloxyethyldimethylbenzylanium chloride (PMBQ) of different molar mass have been used. On silica and Sikron, the adsorbed amounts increase with the ionic strength. The zero point of charge (zpc) and the shape of the zeta potential-pH plots vary with the surface coverage by the polycations. The zeta potentials, diffusion coefficients, and flocculation rates are influenced at different salt concentrations by the adsorbed amounts and characterize the flocculation of the particles. Stabilization is accomplished at low salt concentration for PM and PMBQ near the plateau of the adsorption isotherm by electrostatic repulsion of the covered particles with reverse charge. At high ionic strength, only PM stabilizes the particles sterically by osmotic repulsion of the long tails. For PMBQ, we found a large flocculation range with no stabilization at high coverage. (C) 2000 Elsevier Science B.V. All rights reserved.