Effect of surface charge on the adsorption mode of sodium poly(acrylate) on alumina-coated TiO2 used as coating pigment

The surface properties of TiO2 and alumina-coated TiO2 used as pigments in papers and paints were investigated. The surface characterization of the coated TiO2 product by osmotic stress experiments and surface counterion titration reveals a large proportion of condensed ions which increases with ∣PZC-pH∣. Nevertheless, the number of uncondensed ions for a single particle (related to the effective charge number) remains almost the same for the ∣PZC-pH∣ investigated. This behavior is in agreement with modelisation on other systems. The concept of formal charge introduced by the MUSIC model is combined with the concept of effective charge on an (hydr)oxide surface. A mechanistic description of the adsorption mode of the sodium salt of poly(acrylic) acid (PaNa) on the alumina coated surface at pH 9 is suggested. The results show that only 5–6% of the functional groups of PaNa are linked to the surface and take the place of OH− and presumably Cl− counterions. The PaNa adsorption on this surface at pH 9 is MW independent as expected from theoretical models. The loop-conformation of the adsorbed polymer onto the coated TiO2 surface is deduced.