Abstract: The interfacial tension between oil and water decreases due to the adsorption of ionic liquid surfactant at the interface.The more carbon number of the alkyl chain in the surfactant molecule,the higher ability for decreasing the interfacial tension.Pyridine based surfactants show higher hydrophobicity and higher interfacial tension decreasing capacity than that of imidazole based surfactants.Under existence of high concentration of inorganic salts,capacity of ionic liquid surfactants for decreasing the interfacial tension can be upgraded that achieves about 10^-2 mN/m,which is better than the traditional surfactants.

Key words: surfactant, ionic liquid, interfacial tension, inorganic slat, oil