Functionalized imidazolium-based ionic liquids: Impact on micellar formation and interfacial activity

Interfacial phenomena such as capillary forces, interfacial tension (IFT), and wettability play a key role in controlling fluid flow during oil and gas displacements in porous media. These factors significantly impact the mobility of residual or bypassed oil fractions, especially in challenging reservoir conditions. Ionic liquids (ILs) have shown great potential for enhanced oil recovery (EOR) in depleted and mature reservoirs. However, despite extensive research on ILs families, functionalized ILs remain underexplored in oil recovery. This study focuses on the synthesis and characterization of functionalized IL with acid (–COOH) with particular emphasis on their micellar formation properties and interfacial properties. The critical micelle concentration (CMC) was determined using surface tension and conductivity measurements. To investigate the underlying mechanism of ILs micellization, we employed molecular dynamics (MD) simulations based on the martini force field. Results reveal that –COOH-functionalized ILs reduces CMC by at least tenfold compared to its methylated counterpart. Moreover, oil-water IFT measurements demonstrate superior interfacial activity, with the acid-functionalized ILs lowering IFT below 0.5 mN/m—an uncommon achievement for ILs. MD simulations reveal that the –COOH-functionalized ILs exhibits a high propensity to form faster and larger micelles, primarily due to the presence of ion-pairs within its structure. These ion-pairs enhance ILs micellization by minimizing head-to-head electrostatic repulsion more effectively than the typical counterions. The study highlights the promise of functionalization of ILs, for oil recovery from challenging reservoir conditions, paving the way for new EOR research and applications.