From microscopic nonlinear dynamics to macroscopic friction: low-friction sliding of nanocrystals
KTH Applied Physics seminars
Thursday 15 March 2012
to 10:00 at
Dr Astrid S. de Wijn (Stockholm University)
Structural incompatibility (incommensurability) of two contacting solids leads to low-friction sliding. However, there is experimental evidence that the incommensurate low-friction state of a nanoscale contact is destroyed by rotation of the sliding flake, leading to a commensurate state with high friction.
We study the rotational dynamics and the stability of incommensurate sliding of nanocrystals on crystalline subtrates. By means of a simple, analytically soluble model, we show that stable incommensurate sliding states exist for different types of substrates and nanocrystals, but that their long-term survival under experimental conditions is delicate. We compare our results to experimental data for friction of graphene flakes on graphite and gold crystals on graphite. We propose experimental conditions which produce more robust low-friction states. Using numerical simulations and simple theoretical arguments, we demonstrate how the low-friction states can influence the effectiveness of solid lubrication of macroscopic interfaces with nanocrystals.