The Effects of Ethanol Concentration and of Ionic Strength on the Zeta Potential of Titania in the Presence of Sodium Octadecyl Sulfate

Abstract

Sodium octadecyl sulfate (C18H37SO4Na) induces a negative zeta potential of metal oxides at very low surfactant concentrations as compared with shorter-chained sodium alkyl sulfates. The problem of low solubility of sodium octadecyl sulfate in water was solved by the addition of the surfactant to dispersions as ethanolic stock solution, but then the presence of ethanol in dispersions was inevitable. We demonstrate that the concentration of ethanol (up to 5% by mass) in a dispersion containing titania (TiO2) and sodium octadecyl sulfate has an insignificant effect on the zeta potential of particles. We further demonstrate that the shifts in the IEP of titania induced by the presence of sodium octadecyl sulfate are independent of the NaCl concentration. The results obtained in this study can be generalized for 1-1 salts other than NaCl, for metal oxides other than titania, for organic co-solvents other than ethanol, and for sparingly soluble ionic surfactants other than sodium octadecyl sulfate.