Properties of the ternary mixtures of fluorocarbon and hydrocarbon nonionic surfactants at the water-air interface

Surface tension measurements of aqueous solutions of ternary surfactant mixtures of ethoxylated tert-octylphenol with 10 and 16 ethylene oxide groups, called Triton X-100 (TX100) and Triton X-165 (TX165), respectively, with the fluorocarbon surfactant Zonyl FSN-100 (FSN100) were carried out at 293 K. Based on the surface tension isotherms, the Gibbs surface excess of surfactants concentration at the water-air interface was determined. Then the mole fractions of surfactants in the surface layer were compared with those in the bulk phase. Considering the different composition of the mixed monolayer at the water-air interface, calculated with and without the water content, the molecular interaction parameters of surfactants, their activity coefficients, activity toward water and binary mixtures and the free enthalpy of their mixing were also calculated. As follows from the measurements and calculations, among others, the values of the surface tension of the studied ternary mixture of surfactants at the concentrations corresponding to the saturated monolayer at the water-air interface can be predicted. It is possible to obtain these values on the basis of the monomer mole fraction of TX100, TX165 and FSN100 calculated without the water content at this interface and the values of the surface tension of single surfactants studied at an appropriate concentration. (C) 2013 Elsevier B.V. All rights reserved.