Revealing the behavior of asphaltene at the oil/water interface: influence of resins

In this study, molecular dynamics (MD) simulation is employed to investigate the influence of resins on the behavior of asphaltenes at the oil–water interface, with simulations conducted to capture the dynamic interfacial behavior over a sufficient timescale. It is found that different asphaltene molecules exhibit distinct distribution patterns at the interface, which is closely related to their hydrophilicity. Specifically, asphaltene 1 has a solvation free energy of − 10.36 kJ/mol, with its hydrophilic groups accounting for 38.7% of solvent-accessible surface area. In contrast, asphaltene 2 has a solvation free energy of − 8.44 kJ/mol, and its hydrophilic groups account for 19.7%. Thus, asphaltene 1 is more hydrophilic than asphaltene 2. Correspondingly, asphaltene 1 tends to lie horizontally at the interface and forms more H-bonds with water molecules, whereas asphaltene 2 inserts obliquely into the interface at 60°. The presence of resins significantly regulates the aggregation behavior of asphaltenes. When resins are present, asphaltenes tend to aggregate loosely and exhibit a higher diffusion coefficient [(0.2071 ± 0.0797) × 10⁻⁵ cm²/s] than that in the resin-free system [(0.1539 ± 0.0111) × 10⁻⁵ cm²/s]. Resins enhance the accumulation of asphaltene at the oil–water interface and lead to a 34.6% increase in diffusion coefficient compared to the resin-free system. Moreover, interactions between different resins and asphaltenes vary notably. Resin 5 and resin 6, due to containing heteroatom sulfur, have a stronger binding ability with asphaltenes compared to resins 1–4. The interaction energy between resin 5 and asphaltene 2 is − 1379.66 kJ/mol, indicating a stronger interaction compared to that between resin 6 and asphaltenes 2 (− 809.02 kJ/mol). Consequently, resin 5 and asphaltene 2 form a more stable face-to-face stacking structure, whereas resin 6 forms an unstable T-shaped stacking structure with asphaltenes.