Composition of Multicomponent Surfactant Systems at the Water-Air Interface

Measurements of the surface tension of aqueous solutions of ternary and binary surfactant mixtures of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols), i.e., ethoxylated tert-octylphenol with 8, 10 and 16 ethylene oxide groups, respectively called TOP8, TOP10 and TOP16, 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 and then recalculated for the Guggenheim-Adam surface excess concentration of these substrates. Next the monomer mole fractions of surfactants in the surface layer were determined and compared with those calculated on the basis of both Rosen's approach and the composition in the bulk phase. Taking into account these different values of composition of the mixed monolayer at the water-air interface, the molecular interaction parameters of surfactants, their activity coefficients and the free enthalpy of their mixing were also calculated. As follows from the measurements and calculations, among other things, by the addition of the differences between the values of the mole fraction of surfactants calculated on the basis of Rosen's approach and those determined on the basis of surface excess concentrations, the mole fraction of the solvent at the water-air interface can be determined. Values of the monomer mole fractions of surfactants in the mixed monolayer calculated on the basis of the Rosen's approach and surface excess concentration determined from the Gibbs (X (S) (G)) and Guggenheim-Adam (X (S) (G - A)) equations.