THE PROPERTIES OF MIXTURES OF IONIC AND NONIONIC SURFACTANTS IN WATER AT THE WATER/AIR INTERFACE

Surface tension measurements were carried out for systems containing mixtures of sodium dodecyl sulphonate and Triton X-100. From the results of these measurements we evaluated the molecular interactions parameters for the formation of mixed micelles and mixed monolayers at the water/air interface. Also, the values of the surface tension of the systems studied hale been calculated using a relation derived by Joos (Bull. Sec. Chim. Belg., 76 (1967) 591) and compared with the measured values. From this comparison, the adsorption behavior of the mixture of SDS and TX-100 can be predicted by the Joos relation, and the effect of the molecular interactions in the adsorbed layer at low surface pressure can be neglected; however, near the cmc these interactions should be taken into account particularly if the ratio of TX-100 to SDS in the mixture is low. This is confirmed by the negative values assumed for the interaction parameters. However, no synergism is present in the adsorbed monolayers and in the micelle formation.