Effect of SBS structure on viscosity of SBS-modified asphalt based on molecular dynamics: Insights from shearing phase morphology, adsorption and swelling mechanisms

Optimizing styrene–butadiene–styrene copolymer (SBS) design for pavement engineering is crucial for producing cost-effective SBS modifiers and improving road quality. Five types of SBS molecules were characterized using ¹H NMR. The influence of SBS content and molecular structure on the viscosity and compatibility was explained by molecular mobility, shearing phase morphology, adsorption and swelling behaviors based on molecular dynamics. The results show that the viscosity contribution of SBS is determined by the SBS molecular structure and phase morphology. SBS with longer and more regular chain structure exhibits lower mobility, and a higher propensity for forming network structures, which enhances resistance to the disaggregation of polystyrene (PS) and disentanglement of polybutadiene (PB) during shear. Furthermore, the viscosity contribution of asphalt is determined by the adsorption between SBS and maltenes, as well as the competition between SBS and asphaltenes, which reduces the maltenes mobility and promotes the asphaltenes aggregation. With increasing SBS content, the adsorption strength between SBS and maltenes increases and SBS tends to form a network structure, leading to an increase in viscosity. SBS with high trans-1,4 PB content (SBS-t) exhibits the best viscosity contribution, owing to its exceptionally long and regular molecular chain. High maltenes content or a wide SBS distribution range increase the compatibility. SBS-t has the largest distribution range, resulting in the largest contact area and the best compatibility.