Mixed micelles of polyoxyethylene-type nonionic and anionic surfactants in aqueous solutions

Abstract

Critical micelle concentrations (CMC) and the solubilization toward dyestuff yellow OB in aqueous solutions of mixed polyoxyethylene-type nonionic and anionic surfactants at 30°C were measured. As for the CMC, the stabilization of the mixed micelles relating to polyoxyethylene chains was suggested by application of the pseudo-phase-separation model. Concerning solubilization, the same measurements were also performed for various other surfactant mixed systems, and we defined the solubilizing power of the mixed surfactant solution and the ratio of this quantity to that in the additivity law. Solubilization in the system of mixed polyoxyethylene-type nonionic and anionic surfactants showed a specific behavior as compared with the other systems. From the CMC and solubilization studies, we proposed the model concerning the mixed micelles of polyoxyethylene-type nonionic and anionic surfactants. In the model, polyoxyethylene chains in the mixed micelle have an attracting interaction with anionic head groups, and the interaction is enhanced by the formation of a hydrocarbon core. This status is different from that in free polyethylene glycol and surfactant systems.