Molecular-Atomic Scale Insight on Interface Interaction and Compatibility of Thermoplastic Polyurethane-Modified Asphalt Binder and its Asphalt Mixture via Molecular Dynamics Simulations

Thermoplastic polyurethanes (TPUs) synthesized from different monomers possess diverse chemical structures, leading to variations in asphalt modification performance and an incomplete understanding of the underlying mechanisms. To elucidate the effect of TPU chemical structure on asphalt modification, eight molecular models of asphalt modified by TPU with different chemical structures were constructed, and their mechanical behavior, microstructure, intermolecular interactions, compatibility, and interfacial interaction were systematically investigated by Molecular Dynamic Simulation. The results reveal that the soft segment type is the predominant factor governing the mechanical and interfacial interaction. Asphalt modified with PET-based TPU exhibited higher stiffness, with Young's modulus and shear modulus increasing by 65.04% and 67.44%, respectively, compared with those of PTMEG-based TPU. Moreover, PET-based TPU significantly strengthened the asphalt-aggregate interface, increasing interaction energy by 21.2% relative to PTMEG-based TPU. The maximum interfacial energy of 4165 kcal/mol was obtained for I-PE-M, which was 46% higher than the weakest system. Nevertheless, polyester-based TPUs showed slightly lower compatibility with the asphalt matrix than polyether-based counterparts, indicating a potential trade-off between interfacial enhancement and phase compatibility. These findings elucidate the fundamental colloidal and interfacial mechanisms governing polymer-asphalt systems, providing design principles for optimizing interfacial performance through segmental polarity engineering.