Interfacial bonding enhancement mechanism of sisal fiber cementitious composites via KH560 modification: a multi-scale study combining molecular dynamics and microstructural characterization

The interfacial region between organic fibers and inorganic matrices is often the weakest link in composite materials, and its bonding performance directly determines the macroscopic mechanical properties and long-term service stability. Due to their bifunctional molecular structure, silane coupling agents are widely used for interfacial modification of heterogeneous composites. However, the dynamic mechanism of silane molecules at the organic-inorganic interface remains unclear. In particular, the atomic-scale process by which silane molecules displace the interfacial free water film and construct stable chemical bridges has not been fully clarified. Natural plant fibers are widely used as renewable organic reinforcements in inorganic cementitious composites, but their poor interfacial compatibility remains a common bottleneck. In this study, a sisal fiber-cement matrix system is used as a typical model system, and the combined interfacial enhancement effect of KH560 and silica fume is systematically investigated through multi-scale experiments and molecular dynamics simulations. It should be noted that since silica fume content was kept constant in all groups, the individual contributions of silica fume and KH560 could not be quantitatively decoupled. A proposed ‘dewetting-anchoring-like’ mechanism at the atomic scale is suggested, which can provide theoretical guidance for the interface regulation of similar organic-inorganic composites.