Sedighi M, Svetovoy V B, Palasantzas G
Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands.
Department of Mechanical Engineering, Shahrood University of Technology, Shahrood, Iran.
Phys Rev E. 2016 Jun;93(6):062803. doi: 10.1103/PhysRevE.93.062803. Epub 2016 Jun 24.
Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ∼4-14 nm mainly due to sphere morphology, the relative humidity (RH) ∼0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH∼40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.
