Mechanism of dynamic friction in a humid nanocontact

The physics of dynamic friction on water molecule-contaminated surfaces is still poorly understood. In line with the growing interest in hydrophobic contact for industrial applications, this paper focuses on friction mechanisms in such interfaces. As a commonly used material, contact with graphite is considered in a twin-fold approach based on experimental investigations using the circular mode atomic force microscopy technique combined with molecular dynamic simulations. We demonstrate that an intuitive paradigm should be refined, which asserts that water molecules are squeezed out of a hydrophobic contact. Consequently, we introduce a mechanism considering a droplet produced within the sliding nano-contact by the accumulation of water adsorbed on the substrate. Then we show that a full slip regime of the droplet sliding on the hydrophobic substrate explains the experimental tribological behavior.