PREPARATION OF OXIDE DISPERSIONS WHICH ARE STABILIZED BOTH STERICALLY AND ELECTROSTATICALLY

TiO2 dispersions prepared in the presence of polyacrylic acid (PAA) may be sterically stabilized, electrostatically stabilized, or stabilized by both mechanisms simultaneously, depending on PAA and electrolyte concentrations. Very stable suspensions are obtained when both steric and electrostatic stabilizations occur. PAA adsorption is especially pronounced at low pH, when TiO2 and PAA are oppositely charged. Larger amounts of PAA are effectively adsorbed as neutral molecules since the large concentration of anionic groups near the TiO2 surface cause a large negative electrical potential which exerts a strong attraction on H+ ions. The thickness of the PAA layer was found to be about 3 nm at pH=6 in 0.01 M KNO3 solutions. The results of the experiments suggests that both mechanisms are important and that there is a positive influence of the thin polymer layer on the electrostatic stabilization.