Nano-micelle formation and aggregation in SBS-Modified asphalt induced by π-π interaction using molecular dynamics
Zhiyang Liu, Peng Wang, Zhenfu Huang, Ruibo Ren, Kai Liu
Abstract
Maintaining the storage stability of polymer-modified asphalt is crucial to its optimal performance. The phase separation in styrene-butadiene-styrene (SBS) -modified asphalt during high-temperature storage has not been solved due to the lack of fundamental understanding of intermolecular interaction. This study aims to reveal the formation of molecular nano-micelles and endogenous π-π interaction in the SBS-modified asphalt. Molecular simulation indicates that incorporating more than 7% SBS into bitumen forms SBS self-aggregates that entangle with asphaltenes, causing a reorganization of the colloidal structure. The SBS aggregation is dominated by the π – π conjugate interactions and steric hindrance of confused aromatic. In low-content SBS-modified asphalt (<4%), SBS molecules are constrained by the asphaltenes through Y- and T-shaped π–π conjugates. In high-content SBS-modified asphalt (>7%), SBS interlocks parallel benzene rings and selectively adsorbs maltene from neat bitumen. High concentrations of SBS in the modified asphalt increase inter-SBS attraction but decrease asphaltene-SBS interaction, causing SBS self-aggregation and segregation from asphaltene-rich phase. Atomic force microscope and fluorescence microscope tests demonstrate the selective maltene adsorption and phase migration in high-content SBS-modified asphalt, and macro performance exhibits severe phase separation and degradation. This study provides a new perspective on improving the storage stability of high-content SBS-modified asphalt.