Unexpected solid shear response of liquid-like nanoconfined water films and the effect on friction

Here we find the general and abnormal stick-slip friction of nanoconfined water by extensive molecular dynamics simulations. Specifically, water films exhibit general stick-slip behavior when confined below 1 nm, independent of the water phase, surface wettability, and solid lattice structure. However, at confinement distances of 0.7 and 0.9 nm water films are in liquid-like states, which contradicts the common belief that only solid-like lubricant films can produce stick-slip friction. This unexpected behavior is attributed to the nature of short-time-scale ordered but long-time-scale disordered. Further, we reveal the velocity dependence of friction, which is mainly linear at > = 1 nm, logarithmic at 0.8–0.9 nm, and plateau-like at 0.6–0.7 nm, and give theoretical descriptions by extending the Kramer's theory of activated processes.