Multi-scale synergistic mechanism of ESO-MDI-modified asphalt investigated by molecular dynamics and rheological...

Asphalt pavement is a critical component of transportation infrastructure, and the development of renewable bio-based modifiers offers a promising strategy for improving asphalt performance and sustainability. This research involved the synthesis of three asphalt modifiers (Oxa_1, Oxa_2, and Oxa_3) by regulating the molar ratio between epoxidized soybean oil (ESO) and methylenediphenyl diisocyanate (MDI). The relationship between the modifiers and asphalt properties was analyzed using molecular dynamics (MD) simulations and multi-scale experimental characterizations. The results indicate that the molecular structure of the modifiers significantly influences the performance of modified asphalt. The dual-arm Oxa_2 structure demonstrated the highest degree of physical entanglement and the lowest fractional free volume (FFV), attributable to its symmetrical comb-like configuration, which offers superior resistance to permanent deformation. In contrast, the three-arm star-shaped Oxa_3 enhanced cohesive energy density and complex modulus by introducing a higher density of polar oxazolidinone rings and MDI-derived groups, thereby promoting the formation of a stronger three-dimensional physical cross-linking network. Although Oxa_3 provided the most pronounced improvement in high-temperature stiffness, the single-arm Oxa_1 showed superior low-temperature stress relaxation owing to its higher FFV and greater chain flexibility. Finally, grey relational analysis (GRA) confirmed the close correlation between molecular descriptors and rheological indicators, demonstrating that the molecular architecture of ESO-MDI modifiers governs the multi-scale performance of modified asphalt. This study provides a theoretical basis for the molecular design of sustainable bio-based asphalt modifiers. METHODS: MD simulations were performed using Materials Studio with the COMPASS II force field. Van der Waals interactions were calculated using the atom-based method, while electrostatic interactions were treated using the Ewald summation method. Periodic boundary conditions were applied to eliminate boundary effects. Temperature and pressure were controlled using the Andersen thermostat and Berendsen barostat, respectively.