On the sensitivity of the capillary adhesion force to the surface roughness

Abstract

The adhesion force between rough surfaces in contact is significantly affected by nanoscale asperities. The dominant component of the adhesion force is the capillary force caused by condensed water menisci. The capillary force depends upon the meniscus shape and dimensions. We show, both theoretically and experimentally, that a small change in surface roughness may result in a big change in the meniscus geometry and, consequently, in the adhesion force. This high sensitivity (or instability) of the adhesion force with respect to surface roughness has been overlooked by conventional contact mechanics models that consider adhesion, which assume that the effect of roughness is eliminated with decreasing size of roughness details. The date of atomic force microscopy confirms that the adhesion force between rough surfaces is not a stable function of the roughness.