Dilational Viscoelasticity of the Zwitterionic Gemini Surfactants with Polyoxyethylene Spacers at the Interfaces

The dilational viscoelasticity of zwitterionic gemini surfactants C8ExNC12 with polyoxyethylene spacers at the water-air and water-decane interfaces were investigated by oscillating barriers method. The experiments were carried out at different concentrations with an accessible frequency range of 0.005 to 0.1 Hz. Interfacial tension relaxation method was employed to obtain dilational parameters in a reasonably broad frequency range. Experimental results show that the values of dilational elasticity and viscosity of C8ExNC12 are larger than those of common nonionic surfactants, such as T × 100, and the dilational viscoelasticity at the water-decane is close to that at the water-air interface on the whole. The results may be attributed to Coulombic attraction, and the possible schematic diagrams of adsorbed molecules with different polyoxyethylene spacers at the water-air and water-decane interfaces are proposed. We also analyzed C8ExNC12 from the results of relaxation experiments and Cole-Cole plots.