Molecular Dynamics Investigation into the Self-Healing Mechanisms of Nanosilica Modified Asphalt: Interfacial Diffusion and Thermodynamic Kinetics.

The self-healing capability of asphalt binders is pivotal for mitigating pavement fatigue cracking. To elucidate the enhancement effect of nanosilica on asphalt self-healing, molecular models of neat asphalt (NA) and nanosilica-modified asphalt (NSA) were constructed, and their self-healing behaviors at typical operating temperatures (278-333 K) were systematically investigated using molecular dynamics simulations. The results indicate that NSA exhibits superior interfacial recovery during crack closure. Geometric analyses reveal that structural mismatch at the nanoparticle interface increases the fractional free volume (FFV), yielding a maximum relative diffusion enhancement of 24.5% at 313 K. Thermodynamically, an increased molecular collision frequency offsets the adverse effect of the higher diffusion activation energy caused by steric hindrance, thereby maintaining overall self-healing kinetics. Mechanistically, radial distribution function (RDF) and interaction energy analyses demonstrate that nanosilica possesses a strong adsorption capacity for polar fractions. This characteristic induces a localized competitive adsorption effect that weakens the original asphaltenes/resins interactions by approximately 21%, causing the dissociation of the colloidal structure and thereby effectively enhancing the mobility of resin molecules. These findings provide molecular-level insights into the geometric, thermodynamic, and colloidal mechanisms of inorganic-asphalt systems, offering theoretical principles for optimizing pavement self-healing.