Tribology of interfacial water under nanometer level confinement

COLL 456

J. E. Houston, jehoust@sandia.gov, Surface and Interface Sciences Department, Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185-1415
Interfacial water is important to a wide range of surface processes, including protein folding, the stability of colloid suspensions, enzyme activity and swelling in clays. In this presentation, the results of several studies are discussed concerning the tribological behavior of water under nanometer-level confinement between surfaces functionalized to various levels of hydrophilicity. The studies utilize Interfacial Force Microscopy (IFM) and involve measurements of both the normal and frictional forces as a function of interfacial separation. The results indicate that under bulk water, or even at low humidity, the forces are characteristic of a surprisingly viscous interfacial-water region having a combined thickness of several nm. These results are supported by similar findings using different probing methods and involving several interfacial combinations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.