By growing the demand of energy in the world, attempts to develop new methods in enhanced oil recovery were increased. Among them, chemical enhanced oil recovery (CEOR) methods, with impressive impacts, become more appealing. In other hand, gemini ionic liquids (ILs) are environmentally friendly compounds with high surface/interface activity. In this contribution, current study explores the performance of a homolog series of gemini imidazolium ILs with different alkyl chain lengths, [Cnim-C4-imCn]Br2, n = 4, 8, and 12, for reducing crude oil-water interfacial tension (IFT). In this regard, the influence of pH (within 2.5 - 9.5) and temperature (within 298.2 - 328.2 K) as crucial unit operation parameters were considered. Results showed a drastic IFT reduction in the presence of ILs to the extent of 72.3, 97.8, and 99.97%, respectively, for n = 4, 8, and 12. Results also demonstrate a remarkable synergism by increasing pH, that causes the maximum IFT reduction to the extent of 49.5, 43.1, and 80.3%, for n = 4, 8, and 12. The greater performance of the ILs with pH can be attributed to the hydroxyl ions (OH−) adsorption at the interface and neutralizing electrostatic repulsion between the ILs head groups. Meanwhile, micelles are formed at lower concentrations as pH increases. Also temperature intensified IFT reduction by weakening the molecular forces between phases. The maximum decrease with temperature was about 12.4, 15.2 and 55.7%, for n = 4, 8 and 12, respectively.
