Dynamic adsorption of a gemini surfactant at the air/water interface

• A gemini surfactant, C12C3C12, was synthesized.
• Surface tension of surfactant solution was measured and modelled by a new modelling framework.
• The new model does not require the Gibbs equation or the ionic binding constant.
• Consistent modelling results was obtained at 5 concentrations.

The adsorption of a gemini surfactant, α,ω-bis(N-alkyl dimethylammonium) alkane dibromides, at the air/water interface was investigated by tensiometry. Equilibrium and dynamic surface tension were modelled by a new modelling framework, which is not based on Gibbs adsorption isotherm. The method consistently predicted the dynamic surface tension at five different concentrations and circumvented the uncertainties around the ionic state of the gemini surfactants. It was found that the gemini surfactant had much higher surface affinity, which arose from the double tails, than that of the normal cationic surfactants. The maximum surface excess was consistent with the proposed orientation of gemini surfactant at the air/water interface. The modelling framework provides an effective and consistent method to characterize the interfacial adsorption of gemini surfactants.

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