The lubrication properties of nano-confined liquids underpin countless natural and industrial processes. However, our current understanding of lubricated friction is still limited, especially for non-ideal interfaces exhibiting nanoscale chemical and topographical defects. Here, we use Atomic Force Microscopy to explore the equilibrium and dynamical behavior of a model lubricant, squalane, confined between a diamond tip and graphite in the vicinity of an atomic step. We combine high-resolution imaging of the interface with highly localized shear measurements at different velocities and temperatures to derive a quantitative picture of the lubricated friction around surface defects. We show that defectstend to promote local molecular order and increase friction forces by reducing the number of stable molecular configurations in their immediate vicinity. The effect is general, can propagate over hundreds of nanometers, and can be quantitatively described by a semi-empirical model that bridges the molecular details and mesoscale observations.
Cafolla, C., Foster, W., & Voïtchovsky, K. (2020). Lubricated friction around nano-defects. Science Advances, 6(14), Article eaaz3673. https://doi.org/10.1126/sciadv.aaz3673