Micellization and interaction for ternary mixtures of amino sulfonate surfactant and nonionic octylphenol polyoxyethylene ethers in aqueous solution: 2 blending with nonionic surfactant with a longer or shorter hydrophilic chain

The micellization behavior of the ternary mixture of an amphoteric sodium 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) with two nonionic surfactants, octylphenol polyoxyethylene ether (OP-n, where n is the number of hydrophilic unit oxyethylene glycol ethers, n = 4, 7, 10), was investigated using both the tensiometry and the 1H NMR technique. Also, the effect of the addition of nonionic surfactant with a longer or shorter hydrophilic chain, e.g., OP-10 or OP-4, on the micellization of the binary mixture of C12AS/OP-7 with a maximum synergism was probed. Based on the regular solution theory, thermodynamic models were adopted to obtain the composition, activity coefficient of mixed micelle and some thermodynamic parameters. The addition of OP-10 or OP-4 into the binary mixture of C12AS/OP-7 induces the change in the mixed critical micelle concentration, which can be explained by the change in the composition of mixed micelle and the effect of hydrophilic chain. Thermodynamic data show that the addition of OP-10 or OP-4 results in the change from the enthalpy overwhelming process of micellization to the entropy-driven process. The chemical shift of proton in the terminal hydroxy group of OP-n in binary or ternary surfactant mixture is also adopted to describe the obtained results. The findings will help with understanding the interaction behavior between molecules in the multicomponent mixture, especially, the effect of the addition of homologues or other components on the properties of surfactant formulation.