What is Superlubricity?

Superlubricity is a special material phenomenon in which friction between two materials drops close to zero. True zero friction is not thermodynamically permissible, but superlubricity gets close. This superlubricity phenomenon occurs when two surfaces have crystal lattices which are in incommensurate contact, meaning that the crystal arrangement is such that only a tiny minority of the atoms on the surface come in contact with the opposing surface, generating a vanishingly small amount of friction.

Thus far, superlubricity has been observed most prominently with graphite, though it has also been observed briefly between mica sheets or between a tungsten needle and a silicon or graphite surface. Superlubricity was discovered when physicists studied, at very high precision, the friction force between crystal surfaces. When there is a "lattice mismatch" between two such surfaces, friction can depart almost entirely. This lattice mismatch is achieved simply by playing with the orientation of the crystal layers with respect to one another.

Superlubricity is interesting because it takes place in a dry environment - two crystal faces - rather than the wet environment normally associated with lubricants. In a conventional lubricant, the churning action between lubricant molecules and the adjacent surfaces does actually produce some friction, causing heat, energy loss and material limits. In precisely engineered superlubricant surfaces, this marginal energy loss would practically vanish, making new types of engineering possible. Unfortunately, to ensure the correct orientation and stability of the crystal lattices could require nanoscale engineering, something outside the range of present-day manufacturing.

Superlubricity was coined by relation to the qualities of superconductivity and superfluidity, though it has no real similarities with these. Superlubricity and its study is a relatively recent field, brought up in 1991 but not studied much in the meanwhile. In superconductivity, electricity flows without resistance, and in superfludity, a fluid flows without resistance (friction). Though superfluids are frictionless, similar to superlubricants, the underlying physical mechanism is fundamentally different.