Dispersion of alumina-coated TiO2 particles by adsorption of sodium polyacrylate

The dispersion of alumina-coated TiO2 particles by adsorption of the sodium salt of poly(acrylic) acid (PANa) was investigated in regard to the effective charge number of the particles. The effective surface charge number of the particles as well as the electrokinetic mobility only slightly increase with adsorption of PANa. Osmotic stress experiments have shown that PANa (MW 20 000) loses almost all of its effective charge once adsorbed. Moreover, small angle neutron scattering (SANS) experiments on suspensions at various volume fractions have shown that the structural arrangement of the particles is different in presence of adsorbed PANa only at very short distance (high volume fraction). These experimental evidences lead to the conclusion that the decrease of both the apparent viscosity and initial yield stress after adsorption of PANa can mostly be explained by a steric stabilization. The polyelectrolyte on the surface would prevent the weak but still undesirable aggregation of the particles when they collide.