EFFECT OF ADSORPTION OF NONIONIC SURFACTANT AND NONIONIC ANIONIC SURFACTANT MIXTURES ON SILICA LIQUID INTERFACIAL PROPERTIES

Adsorption of non-ionic surfactants and non-ionic-anionic surfactant mixtures is shown to have marked effects on silica liquid interfacial properties such as hydrophobicity and zeta potential. The hydrophobicity of silica surface is found to be dependent on both adsorption density and structure of the non-ionic surfactants. At relatively low adsorption densities. non-ionic surfactant with long ethoxyl chain (C8-PHI-EO40) is observed to impart hydrophobicity to silica surface, but further adsorption restored hydrophilicity to the silica surface. Such changes in hydrophobicity are not observed with non-ionic surfactant with shorter ethoxyl chain and this difference in hydrophobicity effects is related to the conformational behavior of the adsorbed molecules. Anionic surfactant, which by itself does not adsorb on silica, shows significant adsorption in the presence of the non-ionic surfactant and markedly changes the zeta potential of silica particles. Surfactant adsorption mechanisms responsible for changes in silica liquid interfacial properties are discussed in this paper.