Reverse Stick‑Slip on a Periodic Wedge‑Shaped Micrograting

We have investigated the time evolution of sliding friction between colloidal spheres of PMMA (with diameters of 3 μm and 9.6 μm) supported by an AFM cantilever and a SiO₂ grating consisting of alternated slopes of ± 55° and flat areas, and perio­dicity com­parable or below the sphere diameters. With the larger sphere we recog­nize a repro­ducible 'reverse stick-slip', which is explained by mere momen­tum balance consi­de­ration. The friction is pro­por­tional to the normal load, as expected for elastic contact with a wedge. With the chosen method, a friction coefficient μ ≈ 0.30 and an inter­facial shear strength τ ≈ 0.7 GPa can be esti­mated with no need of force cali­bra­tion. This response is very different from the regular stick-slip with the perio­dicity of the grating, which would be obser­ved if the well-known Prandtl-Tom­linson model for the friction experienced on a periodic potential could be scaled up to the present case.

Publication

Alper Özogul, Stephan Gräf, Frank A. Müller, Enrico Gnecco: "Reverse Stick-Slip on a Periodic Wedge-Shaped Micrograting", Tribology Letters 67 (2019) 29, DOI: 10.1007/s11249-019-1139-xExternal link