Dissymmetric gemini surfactants generated by disulfide exchange in mixed micelles

Abstract

We found the generation of dissymmetric gemini surfactants from symmetric ones in aqueous micelle solutions of gemini surfactants with a spacer containing disulfide linkage. The equilibrium was attained during 5 h incubation at 25 degrees C with 1:2 ratio of symmetric to dissymmetric ones when the total concentrations were sufficiently high compared with monomer concentrations. The generation of dissymmetric form is attributed to the disulfide exchange between the spacer chains, which occurs in the mixed micelles of gemini surfactants with different hydrocarbon chains. The pseudo-phase separation model for micellization was successfully used to predict not only the cmc of binary and ternary mixtures composed of symmetric and dissymmetric gemini surfactants but also the monomer concentrations after the equilibrium. Reversibility of the disulfide exchange was ascertained by the generation of symmetric gemini surfactants from dissymmetric ones.