Polyelectrolyte complexation at oxide-water interfaces influence on colloidal stability

The present study aimed at the colloidal stability at short terms of aluminium oxide particles in aqueous suspensions containing polyacrylic acid and complexing aluminium ions resulting from the oxide dissolution at initial pH 5. Carboxylic acid groups were found to strongly interact with aluminium ions and form a oxide-polymer complex. The kinetics 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 adsorption mechanism was found to depend on the carboxylic acid to aluminium ion ratio. For low value of this ratio, the polyelectrolyte rapidly adsorbed in the form of a polyion highly complexed with the initially solubilized aluminium ions. For high value of the ratio, the adsorption was long delayed and the polyacid underwent an aluminium-hydrogen ion exchange, the extent of which depended on the oxide dissolution rate as evidenced by increase of the pH of the suspension.