Lubrication by molecularly thin water films confined between nanostructured membranes

摘要

We use molecular dynamics simulations to study thermal sliding of two nanostructured surfaces separated by nanoscale water films. We find that friction at molecular separations is determined pri-marily by the effective free energy landscape for motion in the plane of sliding, which depends sensitively on the surface character and the molecular structure of the confined water. Small changes in the sur-face nanostructure can have dramatic effects on the apparent rheology. Whereas porous and molecularly rough interfaces of open carbon nan-otube membranes are found to glide with little friction, a comparably smooth interface of end-capped nanotubes is effectively stuck. The ad-dition of salt to the water layer is found to reduce the sliding friction. Surprisingly, the intervening layers of water remain fluid in all cases, even in the case of high apparent friction between the two membranes.