Adhesion forces measured between particles and substrates with nano-roughness

This report briefly reviews the measurements and interpretation of adhesion forces between microscopic probes and substrates having micro- and nano-scaled roughness characteristics. The measurements were recently conducted at Michigan Technological University using atomic force microscopy. The laboratory study concentrated on both rigid and deformable materials, with the probes larger than the size of roughness features of interacting surfaces. For such systems, a detailed surface characterization, in terms of roughness parameters, asperity size and shape and spacing between asperities, as well as analysis of deformation of materials, is required. Analysis of the experimental data can be done using theoretical models suitable for rough surfaces, which would allow one to normalize the measured forces. Alternatively, loading of the probe during adhesion force measurements can be managed properly to control deformations of the nano-scaled surface irregularities. Controlling the deformation reduces and even eliminates the effects of nano-roughness on the probe-substrate contact area, promoting conditions described by the contact mechanics models for the sphere-smooth substrate system.