Revisiting bitumen-clay interaction using molecular dynamics: The role of surfactants

Abstract

Clay has been extensively applied in the research field of modified bitumen to impart excellent anti-aging properties. However, the tendency of agglomeration and nonuniform dispersion in bitumen compromises its modification effect. Surface functionalization of clay holds promise for addressing this issue by enhancing the bitumen-clay interfacial bonding strength to overcome clay self-aggregation, but it requires a profound understanding of bitumen-clay interactions. To explore the interaction mechanisms between diverse surface functionalized clay (also named organoclay) with bitumen at the molecular level and screen out the best one, this study selected four types of surfactants: cetyltrimethylammonium bromide (CTAB), benzethonium chloride (Byssonium), polyquaternary ammonium salt-11 (PolyQAC-11), and CTAB/3-aminopropyltriethoxysilane (CTAB/APS), for surface functionalization of clay (Expanded vermiculite, EVMT). Molecular dynamics simulations were employed to determine the distribution patterns and diffusion characteristics of bitumen molecules, and the interaction energy of bitumen and clay, as well as the uniaxial tensile performance of the bitumen-clay interface. The results show that variations in types and loadings of surfactants cause distinct distribution patterns of bitumen subfractions at diverse bitumen-organoclay interfaces. Additionally, Byssonium-EVMT and PolyQAC-11-EVMT display a preference for adsorbing aromatics and resins. The introduction of surfactants significantly reduces the diffusion rates of various bitumen subfractions within the interfacial system. In terms of interaction energy, the compatibility of different clay with bitumen can be ranked as follows: Byssonium-EVMT > Na + -EVMT ≈ PolyQAC-11-EVMT > OVEMT > APS-OEVMT. The findings from tensile simulations agree well with the judgments derived from interaction energy, suggesting that Byssonium-EVMT is the optimal choice for surface functionalization, owing to its outstanding interfacial adhesion performance. This study advances the understanding of compatibility between bitumen and clay, providing theoretical insights for the development of clay-modified bitumen with improved compatibility.