MIXED-SURFACTANT SYSTEM OF DODECYLBENZENE SULFONATE AND ALPHA-OLEFIN SULFONATE - MICELLAR AND VOLUMETRIC STUDIES

Critical micelle concentrations of sodium salts of dodecylbenzene sulf onate, alpha-olefin (C-16) sulfonate, and their mixtures have been eva luated by measuring the surface tensions of solutions at 298.15 K. Int eraction parameters for mixed monolayer formation (beta(sigma)) and mi xed-micelle formation (beta(M)) have been calculated from the critical micelle concentration data. Densities of solutions of surfactants;and their mixtures were measured with a vibrating-tube densimeter at 298. 15 K. Apparent and partial molar volumes have been evaluated from solu tion density data. Results of the micellar properties have been explai ned on the basis of a nonideal multicomponent mixed-micelle model. The mixed-surfactant system exhibits synergism in all aspects when the mo le fraction of alpha-olefin sulfonate in the mixture is 0.2. Volumetri c properties correlate well, as the partial molar volumes also show a minimum at the same composition of the mixture. Formation of a compact mixed micelle at this composition has been envisaged.