Are the mixtures of homologous surfactants ideal?

Abstract

The interaction between homologous surfactants in mixed micelles was studied by the Regular Solution Theory of mixed micelles. The interaction is independent of the nature of the polar head groups and attractive and the interaction parameter βM depends linearly on the difference in chain length Δ nC. The interaction becomes ideal at Δ nC = 0.75 ± 0.06. Above Δ nC ≈ 5, the dependence remains linear but the slope increased 2.7 times. The phenomenon is explained as the effect of the reduction of the hydrocarbon/water micelle interface and a better packing of the chains in the micelle core, caused by the inclusion of a shorter homologous surfactants. This reduction can be more effective when Δ nC ≥ 5.