A novel molecularly engineered deep eutectic surfactant from a Gemini ionic liquid and methylurea for EOR utilization: a joint experimental and computational study

Abstract

It is well established that surfactant-assisted enhanced oil recovery (EOR) offers significant advantages for improving oil production efficiency. In this study, a surface-active deep eutectic surfactant (DESU) was synthesized from a Gemini surface active ionic liquid (GSAIL) and methylurea in a molar ratio of 3 : 2, and its potential applications in EOR were systematically investigated. SEM and DLS analyses confirmed the nanoscale size of the synthesized material. FT-IR spectroscopy verified the successful formation of the DESU structure and its stability in the aqueous phase. Density functional theory (DFT) calculations revealed strong hydrogen-bonding interactions and electrostatic stabilization between the imidazolium unit and methylurea molecules, accounting for the pronounced surface activity and observed physicochemical behavior of the DESU. The synthesized DESU effectively reduced the oil–water interfacial tension (IFT) from 27.53 to a very-low value of 0.10 mN m⁻¹ at 328.2 K, demonstrating superior performance compared with its individual precursors or their simple mixture. The experimental IFT data were successfully reproduced using the Frumkin adsorption model with reasonable parameter fitting. Moreover, the DESU promoted the formation of stable water-in-oil emulsions, achieving a maximum emulsion index of 65%, and altered the surface wettability of a quartz plate from oil-wet to water-wet, as evidenced by a contact angle change from 137° to 41°. Overall, these results demonstrate that the designed DESU exhibits remarkable interfacial properties and provides multiple advantages for enhancing the efficiency of EOR processes.