ABSTRACT
A range of surface force methods have been used during the last 25 years for accurate measurements of classical DLVO forces (electrostatic doublelayer and van der Waals forces), polymer-induced forces (steric, bridging, depletion) under a range of solvency conditions, as well as short-range hydration/protrusion forces and long-range attractive forces between nonpolar surfaces in polar solvents. In particular, the interferometric surface force apparatus has been successfully used to probe the liquid structure in the gap between two molecularly smooth surfaces. It is found that the arrangement of the solvent molecules in the gap between the surfaces changes as the surface separation is reduced. Hence, the liquid density in the gap varies and this results in a decaying oscillatory force profile [1] that is detected up to about 10 molecular diameters away from the surface in
the case of rigid and spherical solvent molecules. The range of the structural force is considerably less in liquids composed of more flexible molecules [2,3].
