Synergistic interaction on quasi-binary mixture of amino sulfonate amphoteric surfactant with nonionic diethanolamide induced by glycerol and its concentration

Abstract

Molecular interaction about a quasi-binary mixtures of an amino sulfonate surfactant, sodium 3-(N-dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (DES), with a fatty acid diethanolamide derived from coconut oil (CDA) in aqueous solutions containing both the glycerol of 0.100 mol/L and 0.200 mol/L was investigated using the surface tension measurement. The interfacial parameters indicate that the mixing of DES with CDA can promote the formation of the more compact distribution of molecules adsorbed in the mixed monolayer, the mixing ratio of the mixture induces the difference in the adsorption behaviors at air–liquid interface, and the standard free energy of adsorption at air–liquid interface implies the benefit of adsorption and the change of adsorption behavior based on both the concentration of glycerol in solutions and the mixing ratio in the mixture. In the framework of pseudo-phase separation model, thermodynamic models including the Clint’s model, the Rubingh’s model and the Maeda’s model were employed to effectively estimate the related micellization and thermodynamic parameters. The nonideal mixing of DES with CDA and their synergistic interactions in the mixed micelle depend on both the mixing ratio of the mixture and the concentration of glycerol in solutions. The abundant amount of DES in mixed micelle will result in the absence of synergistic interaction in aqueous solutions containing the glycerol of 0.100 mol/L, and whereas the abnormal case does not again emerge on increasing the concentration of glycerol to 0.200 mol/L. The compatibility in molecular conformation, the steric hindrance, the electrostatic repulsion and the hydrogen-bond formation are adopted to theoretically explain the interaction behavior. Thermodynamic parameters obtained using the Maeda’s treatments also confirm the absence or the presence of synergistic interaction and the formation of stable mixed micelle. These findings will help with understanding the intermolecular behavior and the effect of alcohol concentration.