Deciphering origin of nonmonotonic temperature-dependent sliding friction

This article systematically investigates origin of non-monotonic temperature-dependent friction, characterized by initial decrease and then subsequent rise, forming a friction trough. At low temperatures, thermal excitation generates a small number of phonons which facilitate tip crossing over potential barriers and thus reduce relative barriers and overall friction. However, at high temperatures, increased thermal excitation leads to more phonons which causes atoms on contact surfaces to collide and form higher interface barriers, resulting in greater friction energy dissipation. Further analysis shows that as normal load or sliding velocity increases, position of the friction trough shifts towards higher temperatures due to enhanced nesting degree of interface atoms, which requires more phonons generated at higher temperatures for assisting tip crossing over larger barriers.