Published online by Cambridge University Press: 22 February 2011
As surfaces slide over one another, work is done by the forces causing the motion and energy is lost. Origins of this friction behavior can be very complex and are still scarcely understood in molecular terms. Adhesion, plowing and asperity deformation, heat-induced chemical reactions, viscoelastic response of a sbustrate, and still other influences, can all dominate depending on the physical system in question. Conceptually it is convenient to group these many possible origins of energy dissipation into three categories: elastic and plastic deformation of the underlying substgrates, wear (i.e. degradation of the surfaces and substrates during the course of sliding, and surface mechanical properties of the interface itself. In favorable model systems a substantial degree of separation is possible. This paper is concerned with separating the surface chemical contributions to boundary layer friction from the mechanical ones.