Solubilization in some anionic/cationic surfactant binary systems

The solubilization behaviour of n-heptane, toluene and octan-1-ol in anionic/cationic surfactant binary mixtures was studied. Triethanolammonium dodecylpolyoxyethylene sulfate (TADPS, containing ca 2 ethylene oxide units) was mixed with hexadecyltrimethylammonium bromide (CTABr), dodecylpyridinium chloride (DPC1) or hexadecylpyridinium chloride (CPC1). The synergism for solubilization in those mixtures depended on the polarity of the solubilizate, involving its location in micelles. For n-heptane (non-polar), a practically positive synergistic effect was observed and the maximum additive concentration (MAC) in the TADPS/CTABr system was well predicted by Nishikido's ideal model. For toluene (slightly polarizable), solubilized both in the core and palisade layer of the micelle, a practically positive synergism was noticed. For octan-1-ol (amphipathic) usually solubilized in the palisade layer or forming mixed micelles with surfactants, however, a negative synergistic effect was observed and the partition coefficient between micellar and aqueous phases in the TADPS/CTABr system was well predicted by Treiner's non-ideal model. (C) 2003 Society of Chemical Industry.