Dilational Properties of an Anionic Gemini Surfactant with a Hydrophobic Spacer

The dilational properties of the anionic gemini surfactant, ethanediyl-1,2-bis(sodium N-decanoyl-beta-alaninate), and the comparable conventional surfactant were investigated via the oscillation barrier technique. The oscillation frequency was varied between 0.0033 and 0.1 Hz. The dilational moduli of the gemini surfactant at low surfactant concentration show less dependence on the frequency at the air/water interface compared with the decane/water interface. The interface layer is basically elastic. The dilational moduli at the air/water interface are remarkably higher than those at the decane/water interface. The dilational moduli of the gemini surfactant show two maxima with increasing concentration, originating from the reorientation and compression of the surfactant molecules adsorbed at the interfaces. A possible schematic diagram of the adsorption of the gemini surfactant at the air/water and decane/water interfaces is proposed.