INTERACTIONS IN MIXED INTERFACES OF BINARY SURFACTANT SOLUTIONS

A regular solution model is used to interpret the behavior of binary surfactant mixtures at the liquid/vapor and the solid/liquid interface. Two nonionic surfactants with the general formula H(CH2)n(OCH2CH2)mOH, where m is 4 and 8, are used in three different types of binary surfactant combinations: mixtures of two nonionic surfactants, mixtures of tetradecyl sulfate sodium salt with both nonionic surfactants, and mixtures of dodecyl sulfonate sodium salt with both nonionic surfactants. Two anionic/nonionic mixtures each have the same anionic component, thus giving evidence for correlations between the structure of the nonionic surfactant and the interaction with an anionic component. It can be shown that at the solid/liquid interface, the interaction between the anionic surfactant and the nonionic surfactant with the smaller hydrophilic headgroup is always significantly lower than that between the same anionic component and the nonionic surfactant with the larger hydrophilic headgroup. © 1991.