Rough surface adhesion in the presence of capillary condensation

Capillary condensation of water can have a significant effect on rough surface adhesion. To explore this phenomenon between micromachined surfaces, the authors perform microcantilever experiments as a function of surface roughness and relative humidity (RH). Below a threshold RH, the adhesion is mainly due to van der Waals forces across extensive noncontacting areas. Above the threshold RH, the adhesion jumps due to capillary condensation and increases towards the upper limit of Gamma = 144 mJ/m(2). A detailed model based on the measured surface topography qualitatively agrees with the experimental data only when the topographic correlations between the upper and lower surfaces are considered. (C) 2007 American Institute of Physics.