Molecular Simulations Investigation of Deep Eutectic Solvent Induced Structural and Interfacial Behavior in Surfactant-Enhanced Oil Recovery Systems

Both DES systems significantly reduce interfacial tension, with the IFT decreasing from approximately 12.4 mN/m in the DES-free system to 8.47 mN/m for ChCl/EG and 7.23 mN/m for ChCl/cresol at 30 wt % DES concentration. The ChCl/EG system exhibits a gradual reduction in interfacial tension driven by cooperative hydrogen-bond-mediated restructuring of the aqueous phase and relatively uniform intermolecular ordering. In contrast, the ChCl/cresol system produces stronger interfacial effects at higher concentrations due to the greater interfacial affinity and localized accumulation of cresol molecules near the oil–water boundary.

Hydrogen-bonding and excess entropy analyses further demonstrate that the EG-based DES promotes relatively diffuse and cooperative aqueous structuring, whereas the cresol-based DES induces more localized and concentration-dependent intermolecular organization near the interface. These findings demonstrate that DES chemistry plays a critical role in governing intermolecular organization, hydration structure, and interfacial stabilization in surfactant-assisted c-EOR systems.

The molecular-level insights obtained in this study provide useful guidelines for the rational design of DES–surfactant formulations for EOR applications.