Superlubricity

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Foam in the shape of an egg carton to illustrate the atomic structure of the surface of graphite. Both surfaces are commensurate.
Incommensurability by rotating one surface so that the valleys and mountains no longer lie on top of one another.

Supra lubricity (English: superlubricity ) is a phenomenon in which the friction can almost completely disappear. Superlubricity occurs when two crystalline surfaces slide on top of each other, although dry but inappropriately (see incommensurability from the field of crystallography ). The effect was postulated as early as 1991, but could only be measured with great accuracy between two graphene surfaces in 2004 . The similarity of the term superlubricity with terms such as superconductivity and superfluidity is misleading, since various loss mechanisms can lead to finite (usually small) frictional forces.

The atoms in graphite orient themselves in a hexagonal manner and form an atomic mountain and valley landscape that looks like an egg carton. When the two graphene surfaces are in registry (every 60 degrees) to each other, the frictional force is high. When the two surfaces are rotated out of the registry, the friction is largely reduced. It's like two egg cartons that slide over each other more easily if they are twisted against each other . On a macroscopic scale, this principle could be demonstrated using graphene and diamond-like carbon layers.

An ultra-low friction state can also be achieved when a sharp point glides over a flat surface and the pressure is kept below a certain threshold, depending on the surface potential sensed by the point on the stiffness of the adjacent material. The threshold value can be improved considerably by exciting the slider system at its resonance frequency . This suggests that there is a practical way of limiting wear with NEMS (nanoelectromechanical systems).

Individual evidence

  1. ↑ Martin Dienwiebel, Gertjan S. Verhoeven, Namboodiri Pradeep, Joost WM Frenken, Jennifer A. Heimberg and Henny W. Zandbergen: Superlubricity of Graphite . In: Physical Review Letters . Volume 92, 2004, item number 126101; doi : 10.1103 / PhysRevLett.92.126101 ; PDF .
  2. ↑ Diana Berman, Sanket A. Deshmukh, Subramanian KRS Sankaranarayanan, Ali Erdemir, and Anirudha V. Sumant: Macroscale superlubricity enabled by graphene nanoscroll formation . Science , May 14, 2015 doi : 10.1126 / science.1262024
  3. ↑ Anisoara Socoliuc, Enrico Gnecco, Roland Bennewitz and Ernst Meyer: Transition from Stick-Slip to Continuous Sliding in Atomic Friction: Entering a New Regime of Ultralow Friction . In: Physical Review Letters . Volume 92, 2004, item number 134301; doi : 10.1103 / PhysRevLett.92.134301 .
  4. ↑ Anisoara Socoliuc, Enrico Gnecco, Sabine Maier, Oliver Pfeiffer, Alexis Baratoff, Roland Bennewitz and Ernst Meyer: Atomic-Scale Control of Friction by Actuation of Nanometer-Sized Contacts . In: Science . Volume 313, No. 5784, July 14, 2006, pp. 207-210; doi : 10.1126 / science.1125874 .