NMR study of the interaction between anionic and nonionic surfactants in their mixed micelles. II

Abstract

In the previous work, the interaction of two different surfactants in their mixed micelles has been studied by NMR measurements of System I. The work has been extended to the following Systems II, III and IV: ▪ When the anionic surfactant is added to C 12POE or C 12POES solutions, the proton resonance signal of the polyoxyethylene chain of C 12POE or C 12POES shifts to a higher magnetic field, the extent of the upfield shift depending on the polyoxyethylene chain length and the molar ratio of the two surfactants mixed. This upfield shift of the polyoxyethylene signal can be ascribed to an interaction between the benzene ring of the anionic surfactant and the polyoxyethylene chain of C 12POE or C 12POES. In the first three systems, the degree of the interaction decreases in order of System I > II > III. The upfield shift observed in Systems II and III suggests that the hydrocarbon chains are fairly mobile in the hydrocarbon interior of the mixed micelle. In System IV, the degree of the interaction is smaller than that in System I. This is interpreted as showing that in the mixed micelle, the polyoxyethylene chains of C 12POES molecules are more extended than the chains of C 12POE molecules because of the repulsion of their ionic heads, and the extension of the polyoxyethylene chains is probably less favorable to the interaction with the benzene rings of C 8φS molecules.