Interfacial and micellization behavior of binary mixture of amino sulfonate amphoteric surfactant and octadecyltrimethyl ammonium bromide: Effect of short chain alcohol and its chain length

The interfacial and micellization behavior of binary mixture of an amino sulfonate amphoteric 3-(Ndodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) and a cationic octadecyltrimethyl ammonium bromide (OTAB) were investigated in aqueous solution without or with a 70 g/L alcohol (including methanol, ethanol, 1-propanol and 1-butanol) at 313.15 K by both the tensiometry and the conductometry. The surface excess concentration, the minimum area per surfactant molecule at the saturated interface and the standard free energy of adsorption at the air-liquid interface were adopted to be characteristic of the interfacial adsorption monolayer. Based on the pseudophase separation model and the regular solution theory, the Clint's model and the Rubingh's model was used to obtain the related parameters including the interaction parameters between two surfactant molecules, the compositions and the activity coefficients in mixed micelle and thermodynamic parameters. The effect of the alcohol chain length on the interfacial adsorption and the mixed micellization was discussed. The addition of short chain alcohol influences the properties of mixed cosolvent, the conformation of C12AS molecule and the electrostatic interaction between two surfactant molecules. Thermodynamic data shows that the presence of alcohol with a longer chain is beneficial to form the adsorption monolayer and the mixed micelle, and also it depresses the contribution of entropy to the process of micellization. These findings help with understanding the mechanism on the effect of short chain alcohol on the interfacial and micellization behavior of binary surfactant mixtures and further designing the surfactant formulations. (C) 2021 Elsevier B.V. All rights reserved.