MIXED BILAYERS OF ANIONIC AND NONIONIC SURFACTANTS ON ALUMINA

When nonionic hydrocarbon surfactants with different oxyethylene chain lengths are added to α-alumina previously flocculated by addition of an anionic hydrocarbon or an anionic fluorocarbon surfactant, the flocculated alumina redisperses by the formation of mixed bilayers in such a manner that the hydrophobic chains of the nonionic surfactants are in contact with the anionic surfactant-covered alumina and their hydrophilic groups toward aqueous phase. From measurements of the adsorbed amount of surfactants and of steady-state emission spectra of pyrene solubilized in the mixed bilayers, it is found that the mixed bilayers of anionic hydrocarbon-nonionic hydrocarbon surfactants are formed preferentially to those of anionic fluorocarbon-nonionic hydrocarbon surfactants and that the formation of mixed bilayers occurs more easily with decreasing oxyethylene chain length of the nonionic surfactants. Mean-particle size measurements indicate that the redispersion of alumina with mixed bilayers proceeds more easily with increasing oxyethylene chain length of the nonionic surfactants. © 1990.