Molecular Interactions in Binary Surfactant Solutions: Effect of Ionic Counterpart

The effect of intermolecular interactions on processes of micelle formation and adsorption in binary mixtures of non-ionic Triton X100 (TX100) with ionic sodium dodecyl sulfate and dodecylpyridinium bromide surfactants was studied. The ionic surfactants have identical hydrophobic alkyl chain and different hydrophilic groups. A feature of the used binary surfactant mixtures is that critical micelle concentrations and surface activity of the individual components are considerably different. A synergetic effect of decreasing of the surface tension was found in the surfactant mixtures. It was shown that the mixed adsorption layers and the micellar phases are enriched with the nonionic surfactant. For both sodium dodecyl sulfate/TX100 and dodecylpyridinium bromide/TX100 systems, the synergetic effects were most pronounced at a high molar fraction of the nonionic surfactants in the mixture. By using the Ruben-Rosen model, molecular interaction parameters in the mixed micelles βm, and in the adsorption layers βσ were evaluated. As was shown βm and βσ parameters to be notably higher for sodium dodecyl sulfate/TX100 mixture.