POLYELECTROLYTE COMPLEXATION AT OXIDE-WATER INTERFACES INFLUENCE ON COLLOIDAL STABILITY

The present study aimed at the colloidal stability at short terms of a luminium oxide particles in aqueous suspensions containing polyacrylic acid and complexing aluminium ions resulting from the oxide dissoluti on at initial pH 5. Carboxylic acid groups were found to strongly inte ract with aluminium ions and form a oxide-polymer complex. The kinetic s of polymer adsorption was obtained by determining the concentrations of complexed polyacid or polyacid free of aluminium ion which are non adsorbed and remain in the supernatant as a function of time. The ads orption mechanism was found to depend on the carboxylic acid to alumin ium ion ratio. For low value of this ratio, the polyelectrolyte rapidl y adsorbed in the form of a polyion highly complexed with the initiall y solubilized aluminium ions. For high value of the ratio, the adsorpt ion was long delayed and the polyacid underwent an aluminium-hydrogen ion exchange, the extent of which depended on the oxide dissolution ra te as evidenced by increase of the pH of the suspension.