Interaction of PMANa+ with ZnO and Al2O3 nanopowders: Adsorption, stability and rheological behavior

Commercial Al2O3 and ZnO nanoparticles were modified by low molecular weight polymethacrylic acid sodium salt (PMANa+, Mn = 4000) in aqueous system. The effect of PMANa+ on the adsorption behavior, electrokinetic and rheological properties of Al2O3 and ZnO suspensions was investigated. Adsorption isotherms showed that polymer interaction depended not only on the nature of the surface (AlOH or ZnOH) but also on pH and ionic strength of the suspension. Electrokinetic analysis indicated that adsorption of the polymer is accompanied by a shift in the isoelectric point towards acid pH values. Above a certain concentration, of the order of 2 wt % for Al2O3 and 1 wt % for ZnO, the absolute value of the zeta potential reaches a saturation plateau. The rheological behavior is greatly affected in the presence of added polymer. The viscosity, the storage modulus G′ and the loss modulus G″ of the suspension, decrease and reach an optimum, which depends on both the nature of the solid surface (AlOH or ZnOH) and the pH of the suspension. PMANa+ with Mn = 4000, was found to be a good dispersing polyelectrolyte for both Al2O3 and ZnO nanoparticles owing to electrostatic stabilization.