Effects of additional salts on the interfacial tension of crude oil/zwitterionic gemini surfactant solutions

摘要

Zwitterionic gemini surfactants, which have the advantages of both zwitterionic and gemini surfactants, have been widely used in various disciplines. Sulfobetaine-type zwitterionic gemini surfactants consisting of 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (2C(n)Sb with 6, 8 and 10 carbon atoms) were evaluated for their interfacial activities at the water/crude oil interface. The 2C(10)Sb molecules showed a remarkable ability to decrease the interface tension (IFT) of water/crude oil, and the degree of decrease was much greater than those in either zwitterionic or gemini surfactant systems by at least two orders of magnitude. Furthermore, the effects of salts (NaCl, CaCl2, and MgCl2) on the IFT of the 2C(10)Sb system were thoroughly investigated. Interestingly, the delicate balance between the effects of additional cations and the intramolecular interactions of 2C(10)Sb molecules played crucial roles in the interfacial arrangements of 2C(10)Sb molecules, which were mainly dependent on the bonding abilities of the cations. Moreover, a zwitterionic surfactant and a cationic gemini surfactant were employed in control experiments to verify the proposed mechanisms.