Mechanism on micellization of amino sulfonate amphoteric surfactant in aqueous solutions containing different alcohols and its interfacial adsorption

The process of micellization of amphoteric surfactant sodium 3-(N-dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (C12AS) in aqueous solution without or with alcohols including methanol, ethanol, 1-propanol and 1-butanol and their adsorption behavior at air-liquid interface were investigated with both the tensiometry and the conductometry at 298.15 K. The effect of chain length of alcohol on micellar and interfacial properties were discussed. Some parameters including surface excess concentration (Γmax), minimum area per surfactant molecule (Amin) at air-liquid interface, degree of ionization of micelle, Gordon parameters and cohesive energy density of pure or mixed solvent, and standard free energy of adsorption and micellization, etc. are estimated. At the same amount of alcohol in g/L, the addition of different alcohols changes the values of Γmax, Amin and critical micelle concentration (cmc) of C12AS. Also, the effect of alcohol was discussed. The obtained thermodynamic parameters were used to confirm these behaviors of interfacial adsorption or micellization. These behaviors can be explained theoretically by the change in the polarity or cohesive energy of pure or mixed solvents, the surface charge density of micelle, the partition coefficient of alcohol between micellar pseudophase and intermicellar phase, and the conformation of head group of C12AS on adding alcohol. These findings help with understanding self-assembly behavior of C12AS molecule having electronic delocalization structure at air-liquid interface or in bulk phase and the effect of additives on them, and these results can also provide some information for the design of surfactant formulations and their application in many fields.