Interfacial behavior of SBS in thermoregulation and rheological properties of PUSSP-modified asphalt

s This study aims to enhance the rheological performance of polyurethane solid–solid phase change (PUSSP) modified asphalt by developing a PUSSP/SBS composite system with improved phase stability and thermoregulation. The thermoregulation capacity and heat storage performance of the composites were evaluated through temperature monitoring tests and differential scanning calorimetry (DSC), while the rheological behavior across service temperatures was characterized using a dynamic shear rheometer (DSR) and bending beam rheometer (BBR). In addition, the interfacial interactions and microstructural features were investigated using Fourier transform infrared spectroscopy (FTIR), fluorescence microscopy (FM), and atomic force microscopy (AFM), linking the performance improvement to colloidal structures and surface effects within the asphalt binder. The results reveal that the thermoregulation performance of PUSSP-modified asphalt significantly improves with increasing PUSSP content. During the heating phase, Δ t P-B and Δ T P-B for 10 wt% PUSSP-modified asphalt increased by 54.4 % and 65.5 %, respectively, compared with 5 wt% PUSSP. This enhancement is primarily attributed to the increased heat storage capacity of the PUSSP colloids, which plays a decisive role in thermal regulation. Although PUSSP-modified asphalt demonstrates superior rutting resistance at elevated temperatures, its low-temperature creep resistance is inferior to that of conventional asphalt. At equivalent PUSSP content, the thermoregulation of PUSSP/SBS composite-modified asphalt remains comparable to that of PUSSP-modified asphalt, whereas its rheological properties at both high and low temperatures are markedly improved. Notably, the 5 % PUSSP/5 % SBS composite achieves a PG classification of 82–22. The performance improvement mainly stems from the SBS-induced cross-linking network, which strengthens PUSSP-modified asphalt interfacial bonding and enhances compatibility, micro-elasticity, and crack resistance. Consequently, the cooperative PUSSP–SBS interfacial mechanism achieves a balanced enhancement of rheological and thermoregulatory properties. These findings provide a feasible modification strategy for developing multifunctional asphalt materials, offering meaningful guidance for improving pavement performance in temperature-extreme service environments.