Dilational Properties of Gemini Surfactants with Different Charge at the Interface

The dilational properties of the zwitterionic Gemini surfactant C8E4NC12, cationic Gemini surfactant C12NE3NC12, and anionic Gemini surfactant C8E4C8 with polyoxyethylene spacers at the air/water surface and decane/water interface were investigated by the Langmuir trough method. The influence of concentration on dilational properties was explored. Experimental results showed that C8E4NC12 had higher dilational elasticity and viscosity because of the Coulombic attraction between molecules. The interfacial dilational properties are similar to those of the surface for C8E4NC12. Although C8E4C8 and C12NE3NC12 have the same sign electric charge, the rigid benzene ring of C8E4C8 leads to a different orientation of the long hydrophobic chain on the surface. Therefore, they have different surface dilational properties. Oil molecules can change the interfacial molecular orientation of long. chain alkyl groups, which results in a lower interfacial dilational elasticity and viscosity than that of the surface. Possible schematic diagrams of adsorbed Gemini molecules with different charge at the air/water surface and decane/water interface are proposed. These were verified by the characteristic parameters of the relaxation processes.