Lubrication by molecularly thin water films confined between nanostructured membranes
1 The Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180, USA
2 Laboratory of Chemical Physics, Building 5, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
Revised: 14 September 2010
Published online: 12 November 2010
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 primarily 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 surface nanostructure can have dramatic effects on the apparent rheology. Whereas porous and molecularly rough interfaces of open carbon nanotube membranes are found to glide with little friction, a comparably smooth interface of end-capped nanotubes is effectively stuck. The addition 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.
© EDP Sciences, Springer-Verlag, 2010