Strong Amphiphilic Nature of an Imidazolium Ionic Liquid and 1,3-Dimethylurea Deep Eutectic Surfactant: A Combined DFT and Experimental Study for Enhanced Oil Recovery Applications

A novel deep eutectic surfactant (DESU) was synthesized from an imidazolium-based Gemini surface-active ionic liquid (GSAIL) and 1,3-dimethylurea (DMU) for enhanced oil recovery (EOR) purposes. Density functional theory (DFT) analyses confirmed the spontaneous formation of a strong hydrogen-bonding network between the imidazolium group of the GSAIL and the carbonyl group of the DMU, resulting in a stable supramolecular structure. Energy decomposition analysis (EDA) indicated that electrostatic and orbital contributions dominated over Pauli repulsion, confirming the thermodynamic stability of the product. Further, natural bond orbital (NBO) analysis revealed significant energy delocalization up to 19.32 kCal·mol−1 and a Wiberg bond index within the range of 0.05–0.09, validating interactions that enhance the product’s amphiphilic nature. Results showed that the DESU remarkably reduced the oil–water interfacial tension (IFT) by up to 99.85%, near the critical micelle concentration (CMC). Temperature further lowered the CMC and IFT. The DESU adsorption data matched well with the Frumkin adsorption isotherm model, suggesting strong intermolecular interactions at the interface. Wettability tests demonstrated a significant transition from oil-wet (137°) to strongly water-wet (33°) and that emulsions with 72% stability could be formed after one day and 66% after one week. The results totally confirm the incredible interfacial activity of the DESU.