Molecular-atomic scale insights into polymer-asphalt interactions induced by the oxidation of reactive oxygen species via computational simulation and multifield microscopy characterization

Abstract

The objective of this study is to investigate the intermolecular interactions between polymers and asphalt components due to the oxidation of reactive oxygen species (ROS). Quantum chemistry (QC) and molecular dynamics (MD) were employed to simulate the molecular properties and intermolecular interactions between SBS and asphalt components during ROS aging. Multifield optical microscopy was utilized to analyze the microstructural characteristics and validate intermolecular interactions of SBS and asphalt components during ROS aging. The results show that asphaltenes have the most uneven electrostatic potential (ESP) distribution, followed by resins and aromatics, while saturates exhibit the most uniform ESP distribution. ROS aging leads to a more uneven ESP distribution and a higher polarity for HiMA molecules, especially for asphaltenes and resins with increased formation of polar functional groups. SBS and saturates exhibit small energy gaps and electronic softness, indicating good resistance to ROS oxidation, whereas asphaltenes and resins are prone to free radical oxidation reactions with ROS. The potential ROS oxidation site of asphaltenes and resins are mainly distributed in benzene ring regions and heteroatoms, while that of SBS are primarily located at the polybutadiene chains. The interactions between SBS and asphalt components are primarily driven by van der Waals forces. However, the hydrogen bonding appears after ROS aging, enhancing the intermolecular interactions. The interaction energies of SBS-asphaltenes and SBS-resins are significantly enhanced, and the intermolecular distances are shortened as ROS aging progresses. Multifield microscopy observation reveals that the development of bee structures in polymer regions is significantly faster than that in asphalt regions, indicating a significantly enhanced adsorption of asphaltenes by polymers after ROS aging. This is attributed to the uneven charge distribution, increased polarity, and enhanced reactivity of asphaltenes and SBS due to ROS aging. This study contributes to a molecular-atomic-level understanding of the intermolecular interactions between polymers and asphalt components during ROS aging.