Real-Time Interferometry Study and Molecular Simulation of Adsorption Interaction for Imidazolium Ionic Liquid at Alkane Oil–Water Interface

Ionic liquids (ILs) can act as oil-displacing agents to enhance oil recovery (EOR), and understanding the interaction mechanism of ILs at the oil–water interface is therefore crucial for oil extraction. In this work, the experimental technology of surface interferometry was developed for real-time study of the macroscopic interaction between imidazolium ILs ([C12mim]Br and [C16mim]Br) and octadecane oil. By the interfacial thickness result, kinetic analysis revealed the nonequilibrium dynamic process of diffusion and arrangement for [C12mim]Br interaction but another rearrangement for ([C16mim]Br interaction. The arrangement process was indicated as the limiting step, and the rate order was [C12mim]Br < [C16mim]Br with constant value of |karr([C12mim]Br)| = 0.03 < |karr([C16mim]Br)| = 0.08. By the interfacial mass result, thermodynamic analysis revealed a Freundlich multilayer for [C12mim]Br but a Langmuir monolayer for [C16mim]Br. The interaction spontaneity was indicated as [C16mim]Br > [C12mim]Br with free energy of ΔG[C16mim]Br = –10.67 < ΔG[C12mim]Br = –0.47 kJ mol–1. In addition, molecular dynamics simulation (MDS) was employed to identify the microscopic configurations and energies for the interfacial interaction. The interaction stability was revealed to [C16mim]Br > [C12mim]Br with an energy change of ΔEint([C16mim]Br) = –147.06 kJ mol–1 < ΔEint([C12mim]Br) = –118.85 kJ mol–1 and an overlapped distance of doil–water(3[C16mim]Br) = 11.17 Å > doil–water(3[C12mim]Br) = 9.51 Å> doil–water = 8.88 Å. The interaction mechanism was illustrated by “multilayer hemimicelle stacking” model for [C12mim]Br but “monolayer micelle spreading” for [C16mim]Br. This study establishes a systematic platform for investigating the interaction mechanisms and performance of ionic liquids (ILs) at oil–water interfaces, offering critical insights for reservoir engineering and EOR applications.