A new light on abrasive wear of polymer surfaces

Scientists at OSIM proposed an extension of the well-known Prandtl model for atomic-scale friction

State: 08.07.2019 - 10:00 am

The formation of regular wavy patterns out of compliant soft surfaces scraped by a sharp tip has been observed for about 30 years using atomic force microscopy, but never explained satisfactory so far. In the last issue of Physical Review Letters (doi: 10.1103/PhysRevLett.122.256101) the Gnecco group has proposed an extension of the well-known Prandtl model for atomic-scale friction and applied it to the formation of those structures on a common polystyrene surface. Essentially, the tip is supposed to penetrate the material visco-plastically, while it is pulled elastically along the sample surface. Out of this idea, Prof. Juan J. Mazo and coworkers from the University of Zaragoza have developed and run original numeric simulations in three dimensions. Good agreement has been found between the model results and surface patterns grown up by the PhD students Jana Hennig and Patricia Pedraz under different scanning conditions. Most remarkable are sudden changes in the inclination of the surface waves close to the edges of the scraped area, that the two groups unambiguously relate to boundary effects.

What about new perspectives? It is quite clear that the proposed model is able to predict morphological changes on compliant surfaces scratched in a controlled way. The variety of surface patterns expected as a result of the scanning process is virtually unlimited. Most important, it should be possible to go beyond a single tip and "brush" a surface with an array of nanotips resembling the initial stages of common abrasive wear processes. In this PRL it is also seen that the initial roughness of the surface seems to play a non-negligible role in mitigating the boundary effects. New exciting research and collaborations with the Spanish partner group are in view with other groups interested in joining the effort warmly welcome.