Nanoscale interfacial friction mechanism of swelling clay/concrete or claystone composite under rich-water environment by molecular dynamics simulation

Interlayer water shows a significant and complex influence on the frictional behavior of hydrophilic interfaces. Generally, classical friction theory suggests a positive correlation between friction and normal load, but recent observations have revealed deviations from this trend. Although this discrepancy raises important questions, few studies have conducted in-depth investigations into the underlying mechanisms. Here, we employ molecular dynamics simulations to investigate nanoscale friction mechanisms at saturated clay–clay (homogeneous) and clay–concrete (heterogeneous) interfaces under varying normal stresses, in the context of geological disposal of radioactive waste. Our results reveal fundamentally different frictional mechanisms in the two systems, demonstrating that the influence of interlayer water on friction is primarily determined by the type of hydrogen bonds formed, which in turn depends on the spatial arrangement of water molecules at the interface. Water–solid hydrogen bonds enhance interfacial adhesion and increase frictional strength, whereas water–water hydrogen bonds promote interfacial sliding and act as molecular lubricants during shearing. These findings establish a simple linkage between hydrogen bond type and frictional response, providing molecular-level insights into hydrophilic interface mechanics with implications for both natural and engineered systems.