Control of the zeta potential in semiconcentrated dispersions of titania in polar organic solvents

The electrokinetic potential of commercial titania powder (chiefly anatase) in its 1-10 mass % dispersions in water, lower aliphatic alcohols, and dimethyl sulfoxide (DMSO) is positive, and rather insensitive to the nature of the solvent. The sign of the electrokinetic potential can be reversed to negative by addition of phosphoric acid, or of combination of phosphoric acid with triethylamine or with alkali hydroxide. The critical concentration of surface-active compounds, which induces a sign reversal, depends on the nature of the solvent, and it is higher in organic solvents than in water. The critical surface concentration of surface-active compounds for given organic solvent is rather insensitive to the solid-to-liquid ratio, and typically it is in the range of a few micromoles per square meter. © 2009 American Chemical Society.