ABSTRACT
This chapter describes the most important types of surface forces and the relevant equations for the force laws. Thee attractive forces are stabilized by the hard-core repulsion, and together they determine the surface and interfacial energies of planar surfaces as well as the strengths of materials and adhesive junctions. Whenever an equilibrium force law is required, it is essential to establish that the two surfaces have stopped moving before the “equilibrium” displacements are measured. When displacements are measured while two surfaces are still in relative motion, one also measures a viscous or frictional contribution to the total force. Various surface materials have been successfully used in surface forces apparatuses (SFAs) force measurements including mica, silica, and sapphire. For adhesion measurements in vacuum or inert atmosphere to be meaningful, the surfaces must be both atomically smooth and clean.
