Micellization and Phase Behavior of Binary Mixtures of Anionic and Nonionic Surfactants in Aqueous Media

The micellization and phase behavior of the binary mixed systems comprising the anionic surfactants sodium bis­(2-ethylhexyl) sulfosuccinate (AOT)/sodium alkyl phenol ether sulfate (APES) and nonionic polyoxyethylene alkyl ether surfactants (C10E8/C10E10/C13E10) have been investigated by surface tension, fluorescence spectroscopy, and cloud point measurements. Various micellar characteristics, surface active properties, thermodynamic parameters, aggregation numbers, and Stern–Volmer constants have been evaluated for these systems. Lower cmc values, negative interaction and thermodynamic parameters, higher aggregation numbers, and improved surface active properties for the proposed mixed systems indicate the existence of strong synergistic interactions and the formation of thermodynamically stable mixed micelles. Observed elevation in the cloud point (CP) shift suggests the formation of charged micelles that increases the intermicellar repulsions and poses a hindrance to the coacervation of micelles. It subsequently delays the appearance of the CP and increases the applicability of all these systems over a wide temperature range.