Synergistic Behavior Between Zwitterionic Surfactant α-Decylbetaine and Anionic Surfactant Sodium Dodecyl Sulfate

Here, we present experimental surface tension isotherms of mixed solutions of a zwitterionic surfactant α-decylbetaine (DB) and an anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios. These mixed solutions show a composition dependency with respect to both surface tension effectiveness and critical micelle concentration. The pseudo-regular solution theory has been used to evaluate the interaction parameters in the micelle, β m and at the surface, β s . The results revealed that the mixed solutions of DB/SDS behave synergistically in both surface tension reduction effectiveness and mixed micelle formation at all mole fractions investigated. The values of adsorption area per surfactant molecule at air/solution interface were estimated, which provides some useful information on evaluating the interaction between DB and SDS in mixed adsorbed monolayers. The solubilization behaviors of toluene in DB/SDS mixed solutions were also investigated to help in understanding the structure of mixed micelles of DB and SDS.