Molecular Simulation of the Interaction Mechanism between Natural Rubber and Modified Asphalt

Molecular dynamics simulations were used to investigate how natural rubber and its vulcanization state affect asphalt microstructure and intermolecular interactions. Three systems—virgin asphalt, unvulcanized natural rubber (NR)-modified asphalt, and vulcanized natural rubber (VNR)-modified asphalt—were compared in terms of component interactions, molecular mobility, and packing characteristics. Van der Waals interactions dominated rubber–asphalt interactions. Compared with NR, VNR exhibited a lower interaction energy magnitude with asphaltenes but a higher magnitude with resins, indicating that the prescribed sulfur modification altered component-specific interactions. NR inhibited asphaltene migration, whereas vulcanization modified the component diffusion behavior. The free volume fractions of virgin, NR-modified, and VNR-modified asphalt were 17.74 %, 16.33 %, and 17.10 %, respectively, indicating that NR produced the most compact packing, whereas VNR retained more free space than NR. The corresponding average numbers of hydrogen bonds were 332, 352, and 381, indicating increased hydrogen bonding within the simulated modified systems. These results demonstrate that vulcanization influences both molecular packing and intermolecular association, providing molecular-level insights into the design of natural rubber-modified asphalt.