DEFORMATION OF SURFACES DUE TO SURFACE FORCES

Surface deformations are often observed during the course of surface force experiments. We have calculated these deformations from continuum elastic theory for three fundamental types of surface force: attractive van der Waals interactions, electrical double layer repulsions, and oscillatory solvation forces. Strong repulsive surface interactions cause the surfaces to flatten, whereas the surfaces bulge out toward one another under the influence of strong attractive forces. The Derjaguin approximation, which relates the force scaled by the undeformed radius of curvature of the surfaces to the interaction free energy between planar plates, cannot be used when the surface deformations are large. The error in the free energy when the Derjaguin approximation is used is shown for the different force laws.