The influence of surfactant impurities on colloid stability and dispersion of powders in aqueous suspensions

Surfactants have been used for different industrial and cosmetic purposes for decades. Most industrial formulations are complex mixtures of many different chemicals. Often, more than one component is surface active. In this paper we present the results of studies on the colloid stability and dispersion of metal oxide powders in anionic surfactant solutions with nonionic or long chain anionic surface-active impurities. Dodecanol dramatically influenced anionic surfactant adsorption and powder dispersion in mixed surfactant solutions. The enhancement of anionic surfactant adsorption modified the colloid stability of dispersed metal oxides. At the same concentrations where powders were flocculated in the presence of pure anionic surfactants, stable dispersions were observed after addition of less than 1 wt.% of dodecanol, Similar effects were observed in the presence of 1 wt.% of long chain anionic surfactant impurities. The modified flocculation/dispersion behavior is caused by the enhanced coadsorption of nonionic and anionic surfactants at the oxide-water interface, Even more interesting behavior was observed at pH values above the isoelectric point of oxides where particles and surfactants bare negative charge. Pure anionic surfactants cannot stabilize oxides at such pH values, but mixtures containing less than 1 mol% of dodecanol significantly stabilized hematite and anatase at pH values above the isoelectric point. (C) 1998 Elsevier Science S.A. All rights reserved.