Equilibrium adsorption layer characteristics of mixed sodium dodecyl sulphate/Triton solutions

The adsorption of the anionic surfactant SDS in mixtures with non-ionic surfactants of the Triton type (X-45, X-100, X-165, X-405) is studied by bubble profile analysis tensiometry at the solution/air interface. The surface tension isotherms are described by a thermodynamic model for mixed surfactants which allows consideration of different adsorption models for the two compounds: a reorientation model for the Tritons and a Frumkin model for SDS. The experimental data are very well described by the model while for the mixtures the characteristic parameters of the single compounds have been used.

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► Bubble profile tensiometry is suitable for adsorption studies at low surfactant concentration.
► SDS and Tritons follow the Frumkin model and the reorientation model, respectively.
► A thermodynamic model allows to describe the adsorption of these mixed surfactant layers.
► The competitive adsorption of SDS and Triton leads to changes in surface layer composition.
► Peculiarities are explained by a gradually displaced of the ethylene oxide chain from the surface.