Dr. Astrid S de Wijn, SU

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[1], 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[2].  We compare our results to experimental data for friction of graphene flakes on graphite[1] and gold crystals on graphite.  We propose experimental conditions which produce more robust low-friction states[3].  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 [4].
 

[1] A. E. Filippov, M. Dienwiebel, J. W. M. Frenken, J. Klafter, M. Urbakh: Torque and twist against superlubricity.  Phys. Rev. Lett. 100, 046102 (2008).
[2] Astrid S. de Wijn, C. Fusco, and Annalisa Fasolino, Stability of superlubric sliding on graphite, Physical Review E 81, 046105 (2010).
[3] Astrid S. de Wijn and Annalisa Fasolino, Stability of low-friction surface sliding of nanocrystal with rectangular symmetry and application to W on NaF(001), Tribology Letters 39, 91 (2010).
[4] A. S. de Wijn, A. Fasolino, A. E. Filippov, and M. Urbakh, Low friction and rotational dynamics of crystalline flakes in solid lubrication, Europhysics Lett. 95, 66002 (2011