Micellar evolution in mixed nonionic/anionic surfactant systems

Surfactant mixtures are widely used in industrial applications due to their favorable synergistic interactions. For instance, anionic and nonionic mixtures are often employed in detergent, personal care, and enhanced oil recovery. It is useful to understand micellization behaviors of such mixtures, as they are important for formulation optimizations. A range of techniques including surface tensiometry, fluorescence spectroscopy, ultrafiltration, and analytical ultracentrifugation (AUC), were employed in this work to obtain information on the micellization behaviors of the mixed n-dodecyl-β-D-maltoside (DM)/sodium dodecyl sulfonate (SDSN) system. The interaction parameter, monomer concentration, and micellar size and shape distribution were obtained for this mixed surfactant system as a function of total surfactant concentration as well as mixing ratio to achieve a full understanding of their aggregation behaviors. The coexistence of two types of micelles was identified in this mixed anionic/nonionic surfactant system for the first time. A model is proposed to explain such coexistence based on the surface activities and the interactions between the two types of surfactants. These findings are useful for optimizing the composition of mixed surfactant systems and enhancing the synergetic efficiency of the system to achieve more effective and economical formulations.