Effect of surface roughness on sliding friction of micron-sized glass beads

In order to understand the contact phenomena of micron-sized particles, which have a tremendous impact on a variety of applications in industry and technology, direct access to the loads as well as the displacements accompanying such contacts are mandatory. Typical particle ensembles show a size variation ranging from the nanometer to the tenths of micron scale. Especially the contact behavior of particles featuring radii of several up to several tenths of microns is scarcely studied as these particles are typically too large for atomic force microscopy (AFM) based approaches and too small for conventional macroscopic testing setups. In this work a nanoindenter based approach is introduced to gain insight into the contact mechanics of micron-sized glass beads sliding on rough silicon surfaces at various constant low normal loads. The results are analyzed by a simple modified Coulomb friction law, as well as Hertz, JKR, and DMT contact theory.