Short-Range Exponential Repulsive Force Between Randomly Rough Surfaces

Using a Surface Forces Apparatus we have studied the effects of surface roughness on the interaction forces and deformations of polymeric surfaces. We measured the force-distance functions on approach and separation of two rough surfaces which, on approach, exhibited an almost perfect exponentially repulsive force-distance regime, and a weak adhesion on separation. Random roughness may be a prerequisite for the exponential force regime, which appears to be due to the local compressions (micro- or fine- grained deformations) of the surface asperities. The resulting characteristic decay lengths were fitted to common surface roughness parameters obtained by Atomic Force Microscopy to draw possible correlations. The coarse-grained (global) deformations of the initially curved surfaces appear to be Hertzian.