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 cm ² /s] than that in the resin-free system [(0.1539 ± 0.0111)×10 ^− 5 cm ² /s]. Resins make asphaltene more inclined to accumulate at the oil-water interface. 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 asphaltenes 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.