Superlubricity


Superlubricity

Superlubricity is a regime of motion in which friction vanishes or very nearly vanishes.

Superlubricity may occur when two crystalline surfaces slide over each other in dry "incommensurate" contact. This effect, also called "structural lubricity", was suggested in 1991 and verified with great accuracy between two graphite surfaces in 2004 ["Superlubricity of Graphite" Martin Dienwiebel, Gertjan S. Verhoeven, Namboodiri Pradeep, Joost W. M. Frenken, Jennifer A. Heimberg, and Henny W. Zandbergen Phys. Rev. Lett. 92, 126101 (2004) DOI|10.1103/PhysRevLett.92.126101 [http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf] ] .The atoms in graphite are oriented in a hexagonal manner and form an atomic hill-and-valley landscape, which looks like an egg-crate. When the two graphite surfaces are in registry (every 60 degrees), the friction force is high. When the two surfaces are rotated out of registry, the friction is largely reduced. This is like two egg-crates which can slide over each other more easily when they are "twisted" with respect to each other.

A state of ultralow friction can also be achieved when a sharp tip slides over a flat surface and the applied load is below a certain threshold. Such "superlubric" threshold depends on the tip-surface interaction and the stiffness of the materials in contact, as described by the Tomlinson model [" Transition from Stick-Slip to Continuous Sliding in Atomic Friction: Entering a New Regime of Ultralow Friction" Anisoara Socoliuc, Enrico Gnecco, Roland Bennewitz, and Ernst Meyer Phys. Rev. Lett. 92, 134301 (2004) DOI|10.1103/PhysRevLett.92.134301 ] .The threshold can be significantly increased by exciting the sliding systemat its resonance frequency, which suggests a practicalway to limit wear in nanoelectromechanical systems ["Atomic-Scale Control of Friction by Actuation of Nanometer-Sized Contacts" Anisoara Socoliuc, Enrico Gnecco, Sabine Maier, Oliver Pfeiffer, Alexis Baratoff, Roland Bennewitz, and Ernst Meyer Science 313, 207 (2006) DOI|10.1126/science.1125874 ] .

In any case, one should note that the similarity of the term "superlubricity" with terms such as "superconductivity" and "superfluidity" is misleading; other energy dissipation mechanisms can lead to a finite (normally small) friction force.

ee also

* Friction force microscopy
* Tomlinson model

References

External links


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