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.

Graphical abstractThe comparison of the calculated on the basis of the Sprow and Prausnitz equation values of the activity of the aqueous solution of the single fluorocarbon surfactant FSN100, in the ternary mixture with the hydrocarbon surfactants, TX100 and TX165, where the mole fraction in the bulk phase of TX100 = 0.3, TX165 = 0.2 and FSN100 = 0.5 as well as in the ternary mixture with the hydrocarbon surfactants at the constant TX100 and TX165 concentration calculated toward water and toward the binary mixture of TX100 and TX165 at the total concentration of aqueous solution equal to 10−5 and 2 × 10−5 M.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The area occupied by the FSN100 molecule in the mixed monolayer at the water–air interface is higher than that of single solution. ► The presence of FSN100 decreases the adsorption of TX100 and TX165 at the water–air interface. ► There is a synergetic effect in the reduction of water surface tension by the mixture of TX100, TX165 and FSN100.