Superlubricity
Encyclopedia
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.
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
.
The threshold can be significantly increased by exciting the sliding system
at its resonance frequency, which suggests a practical
way to limit wear in nanoelectromechanical systems
.
In any case, one should note that the similarity of the term superlubricity with terms such as superconductivity
and superfluid
ity is misleading; other energy dissipation mechanisms can lead to a finite (normally small) friction force.
Regime
The word regime refers to a set of conditions, most often of a political nature.-Politics:...
of motion in which friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
vanishes or very nearly vanishes.
Superlubricity may occur when two crystalline surfaces slide over each other in dry incommensurate
Commensurability
Two concepts or things are commensurable if they are measurable or comparable by a common standard.Commensurability may refer to:* commensurability , the commensurability of scientific theories...
contact. This effect, also called structural lubricity, was suggested in 1991 and verified with great accuracy between two graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
surfaces in 2004.
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
Tomlinson model
Also: Prandtl-Tomlinson-Model. One of the most popular models in nanotribology widely used as the basis for many investigations of frictional mechanisms on the atomic scale. Essentially, a nanotip is dragged by a spring over a corrugated energy landscape. A "frictional parameter" η can be...
.
The threshold can be significantly increased by exciting the sliding system
at its resonance frequency, which suggests a practical
way to limit wear in nanoelectromechanical systems
Nanoelectromechanical systems
Nanoelectromechanical systems are devices integrating electrical and mechanical functionality on the nanoscale. NEMS form the logical next miniaturization step from so-called microelectromechanical systems, or MEMS devices...
.
In any case, one should note that the similarity of the term superlubricity with terms such as superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
and superfluid
Superfluid
Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...
ity is misleading; other energy dissipation mechanisms can lead to a finite (normally small) friction force.