Activity and thermodynamic parameters of some surfactants adsorption at the water–air interface

Measurements of the surface tension of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethylethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide were made at different temperatures. On the basis of the obtained results the activity of the surfactants at the water–air interface was determined and discussed based on the intermolecular interactions. The surfactant activity at the water–air interface was taken into account for determination of thermodynamic parameters of surfactant adsorption using the Langmuir method and the Szyszkowski equation. The thermodynamic parameters were also determined by means of the Rosen and Aronson, Gamboa and Olea methods as well that based on the changes of tail–water interface tension to that of tail–air.

The free enthalpy of adsorption, ΔGadso, of SDDS, CTAB and TX-100 at the water–air interface determined by different methods at 293 K.Figure optionsDownload as PowerPoint slideHighlights
► Surfactant activity in surface layer can be predicted on the basis of water activity in the bulk phase.
► The standard free enthalpy of surfactants adsorption can be predicted from their surface tension.
► RT in Langmuir equation is more appropriate for ionic surfactants than 2RT.