Effect of inorganic salt on the aggregation in aqueous solution and interfacial activity of symmetrical 1,3-dioctylimidazolium ionic liquids

1,3-dioctylimidazolium ionic liquids ((C8) 2 mimAc) with acetate anions was synthesized and characterized by 1 H NMR, FT-IR, and TGA. The effect of inorganic salt (NaCl, CaCl 2 , and MgCl 2 ) on their solution properties and interfacial activities were systematically investigated using surface tension, dynamic light scattering (DLS), oil–water interfacial tension, and contact angle. The results showed that the addition of NaCl and MgCl 2 can decrease the critical micellar concentration (cmc) values and surface tension at the cmc. However, the distribution of (C8) 2 mimAc molecules at the air–liquid interface is reduced, and the formation of aggregates in the aqueous solution is increased by CaCl 2 . Interfacial tension and contact angle tests showed that the ability of inorganic salts to enhance oil–water interfacial activity and wettability of (C8) 2 mimAc followed the order: NaCl < MgCl 2 < CaCl 2 , which is meaningful for the application of (C8) 2 mimAc in enhanced oil recovery.