Interfacial stiffness and adhesion of randomly rough contacts probed by elastomer colloidal AFM probes

We report on contact mechanics experiments addressing the role of surface roughness on interfacial stiffness and adhesion. Colloidal atomic force microscopy probes, based on poly(dimethylsiloxane) microparticles, are pressed against ceramic substrates with different roughnesses; the applied load, deformation rate and dwell time being separately controlled. We observe a clear dependence of load-deformation curves and pull-off forces on roughness values, likely arising from morphological modulation of the contact area; remarkably this affects the contact stiffness, which is found to decrease for rougher junctions. The emergence of purely geometrical effects for poly(dimethylsiloxane) rough contacts extends previous findings on plastically deformed self-affine surfaces and demonstrates the efficient tuning of contact response through a proper design of surface morphology.