Studies of the influence of polyelectrolyte adsorption on some properties of the electrical double layer of ZrO2-electrolyte solution interface

An influence of the molecular weight of the polymer and inorganic contamina tions of zirconia on the adsorption and electrokinetic properties on ZrO2-e lectrolyte solution interface was studied. Two polymers were used; polyacry lic acid (PAA) and polyacrylamide (PAM). On the basis of the obtained depen dencies, main factors responsible for observed changes of zeta potential an d surface charge of washed and contaminated ZrO2 were determined. It was sh owed, that the change of ionic structure in the Stem layer depends on the n umber and arrangements of -COOH groups in PAA and PAM macromolecules. These groups are responsible for the conformation of polymer chains near the sur face and have direct influence on the amount of the adsorbed polyelectrolyt e. The inorganic ions, present on the surface of the oxide, blocking some p art of active sites, making them inaccessible for adsorbing by carboxylic g roups polymer chains. That makes the adsorption on the contaminated oxide l ower than on the washed one. From the comparison of the determined values of the diffuse layer charge an d surface charge, the main factor influencing the zeta potential changes at different pH, molecular weight and polymer concentration was determined. A lso was demonstrated, that the contaminations of the solid are reason for c onsiderable shift of pH(pzc) in relation to pH(iep) of the zirconia. Thickness of the adsorption layers and free energies of the adsorption of p olyacrylic acid and polyacrylamide on the surface of ZrO2 were calculated.