Simulation and experimental investigation of the microstructural characteristics of nano-TiO2 modified asphalt

Abstract

Nano-TiO2 modification affects asphalt at both molecular and surface scales, yet the relationships among interfacial interactions, cluster mobility, surface morphology, and local nanomechanical response require further investigation. This study combined molecular dynamics (MD) simulations and atomic force microscopy (AFM) to investigate asphalt containing 10, 15, and 20 wt% anatase TiO2. The MD models contained TiO2 clusters of 0.6–1.2 nm, while the experimental binders were prepared using 3–5 nm anatase particles. Interaction energies were negative in all four asphalt-fraction submodels, ranging between −35.23 and −25.13 kcal mol−1, indicating attractive interactions within the constructed systems. The calculated diffusion coefficients exhibited non-monotonic variations with cluster size and TiO2 dosage. At 20 wt%, increasing the temperature from 25°C to 165 °C increased the diffusion coefficient of the 0.6 nm cluster from 2.08 × 10−7 to 8.04 × 10−7 cm2 s−1, whereas that of the 1.2 nm cluster changed from 1.70 × 10−7 to 1.76 × 10−7 cm2 s−1. AFM measurements also revealed a non-monotonic roughness response. The Ra values were 4.43, 3.97, 4.24, and 2.32 nm, and the corresponding Rq values were 9.16, 7.93, 8.32, and 4.04 nm for the 0, 10, 15, and 20 wt% formulations, respectively. Adhesion and energy-dissipation maps indicated enhanced local responses at 10–15 wt%, followed by lower and more spatially heterogeneous responses at 20 wt%. These findings characterize the size-, dosage-, and temperature-dependent microstructural responses of TiO2-modified asphalt and provide a molecular- and surface-scale basis for subsequent evaluation of its functional performance.