Study of electrokinetic properties and structure of adsorbed layers of polyacrylic acid and polyacrylamide at Fe2O3-polymer solution interface

Influence of polyacrylic acid (PAA) and polyacrylamide (PAM) molecular weight on adsorption and electrokinetic properties of Fe2O3-polyelectrolyte solution interface was studied. Main factors, responsible for observed changes of zeta potential and surface charge of hematite, were determined on the basic of obtained data. It was demonstrated that number and the distribution of -COOH groups in PAA and PAM macromolecules decides on the polymer chain conformation at the interface and directly influences of the adsorption amount of both polyelectrolytes. Using zeta potential the free energies of adsorption of PAA and PAM on surface of Fe2O3 were determined. The thickness of polymer adsorbed layers were calculated basing on measurements of the suspension viscosity, compared to viscosity of polymer solution. It was proved that adsorption layer thickness increases with the increase of the polymer molecular weight, pH and concentration of the polymer solution. Using Scheutjens-Fleer model of polymer adsorption the participation of segments as trains, loops, tails was computed. From the above data a structure of adsorbed polymer layers was proposed. The comparison of determined values of diffuse layer charge with surface charge allow learn main factors responsible for zeta potential changes as a function of polymer molecular weight, pH and concentration of the polymer solution. (C) 2002 Elsevier Science B.V. All rights reserved.