Study on the mechanism of hydroxylated carbon nanotubes enhancing the high temperature performance of SBS asphalt by nano-bridging

To cope with the severe challenge posed by extreme high-temperature climates to asphalt pavements, hydroxylated carbon nanotubes (CNTs) were introduced into SBS-modified asphalt as nano-reinforcements in this study. The enhancement mechanism was deeply explained by a multi-scale approach combining macroscopic rheology and molecular dynamics simulation. Rheological tests indicated that an appropriate CNT dosage significantly improved the high-temperature stability of the asphalt and reduced its viscosity-temperature sensitivity, whereas excessive CNTs led to performance degradation due to nano-aggregation. This dosage dependency of macroscopic performance corresponded well with the microstructural evolution observed by fluorescence microscopy: with the increase of CNT content, the SBS phase gradually evolved from a continuous filamentous network into finely and uniformly dispersed phase domains, ultimately leading to phase separation at high dosages. Molecular dynamics simulations further reveal the microscopic mechanism of the above evolution at the molecular level. Hydroxylated CNTs form strong hydrogen bonds with resins through surface hydroxyl groups, which selectively disrupts the thermodynamic equilibrium of asphaltene-resin micelles and creates conditions for the refinement of SBS phase. Simultaneously, CNTs effectively restrict the high-temperature thermal motion of SBS segments and enhance interfacial adhesion with the asphalt matrix by their nano-bridging effect, thereby establishing a robust microstructural foundation for the optimization of macroscopic performance. These findings clarify the structure-property relationship of CNTs/SBS modified asphalt, providing a theoretical basis for the precise design of high-performance composite modified materials.