Everything about Superlubricity totally explained
Superlubricity is a
regime in which
friction vanishes or very nearly vanishes. Superlubricity occurs when two crystalline surfaces slide over each other in dry,
incommensurate contact. It is an effect that has been already suggested in
1991 but has recently been measured with great accuracy between two
graphite surfaces. 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.
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're "twisted" with respect to each other.
A state of ultralow friction is also reached when a sharp tip slides over a flat surface and the applied pressure is below a certain threshold, depending on the surface potential sensed by the tip and the stiffness of the contacting materials.
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.
Further Information
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