Effect of isopropanol on the micellization of binary mixture containing amino sulfonate amphoteric surfactant in aqueous solution: Mixing with octylphenol polyoxyethylene ether (7)

Abstract

A systematic investigation of the effect of isopropanol (IPA) on the micellization of binary mixtures of an amphoteric surfactant, sodium 3-(N-dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (C12AS), with a nonionic surfactant, octylphenol polyoxyethylene ether having seven oxyethylene glycol ether (OP-7), the interaction between them, and thermodynamic parameters was performed in the water-IPA mixed solvent media (the concentration of IPA in bulk solution is within the range of 0 to 100g/L) at 25±0.2°C. The values of critical micelle concentration (cmc) of individual surfactants and their mixtures were determined by both the tensiometry and the UV–vis spectrometry. According to the pseudophase separation and other theromdynamic models (including Clint's model, Rubingh's model, Maeda's model, etc.), molar fractions of components and activity coefficients in mixed micelle, interaction parameters between two surfactants, and thermodynamic parameters were calculated from the corresponding relationships. The variation of the cmc and the micellization parameters with the concentration of IPA can be explained by the structure-breaking ability of IPA and the change in the conformation of C12AS. The synergistic effect between two surfactants can be observed and has a strong dependence on the concentration of IPA. Thermodynamic data show that the micellization for the C12AS/OP-7 mixture is a entropy-driven spontaneous process. The addition of IPA is a disadvantage to the formation of mixed micelle. In comparison with the case in aqueous solution without IPA, the presence of IPA causes a remarkable contribution of entropy to the process of micellization and the contribution increases with the concentration of IPA.