Adsorption of mixtures of sodium dodecyl sulphate and propanol at water–air and polytetrafluoroethylene–water interfaces

A straight linear relationship was found between the adhesion tension and surface tension of aqueous solution of surfactant and alcohol mixtures at a given constant concentration value of SDDS, and the slope of the obtained straight lines was equal to −1, which suggests that the surface excess of the surfactant and alcohol mixture concentrations at polytetrafluoroethylene (PTFE)–water interface is the same as at water–air interface for a given bulk concentration of these mixtures. It was also found that the changes of the surface tension of the aqueous solution of SDDS and propanol mixtures and PTFE-solution interface tension as a function of SDDS and propanol concentration result especially from decreased contribution of the polar intermolecular interactions in the surface and interface tensions and can be described by modified Szyszkowski equation. The analysis of the excess of SDDS and propanol concentration at PTFE–water interface based on results of the surface tension and contact angle measurements suggests that this excess is not a linear function of the mixture composition and that polar interactions can probably take place at the interface of PTFE-aqueous solution of the surfactant and propanol mixture.