Transitions between nanomechanical and continuum mechanical contacts: new insights from liquid structure.

The use of continuum mechanics to describe contacts involving nanoscale and atomic interactions has been one of the key controversies in nanoscience, tribology, and petrophysical and geological studies. By applying a novel nonequilibrium molecular dynamics scheme to wet quartz contacts, this study revealed the key transitions between continuum electrostatic, nanomechanical and Hertzian contact behaviors at around one nm of surface separation, which results in critical contact pressure fluctuations between -30 and 100 MPa. Using a novel liquid-structure analysis scheme based on the spatial distribution of water molecules, the nanomechanical behavior was found to originate from the collapse and localization of layers of water molecules. Moreover, the role of surface curvature on this effect was also quantified and explained based on a new topological descriptor. The findings of this study enrich our understanding of wet contacts and have a wide range of applications from the nanoscale to macroscale.