Abstract
The possibility to achieve entirely frictionless, i.e., superlubric, sliding between solids holds enormous potential for the operation of mechanical devices. At small length scales, where mechanical contacts are well defined, Aubry predicted a transition from a superlubric to a pinned state when the mechanical load is increased. Evidence for this intriguing Aubry transition (AT), which should occur in one dimension (1D) and at zero temperature, was recently obtained in few-atom chains. Here, we experimentally and theoretically demonstrate the occurrence of the AT in an extended two-dimensional (2D) system at room temperature using a colloidal monolayer on an optical lattice. Unlike the continuous nature of the AT in 1D, we observe a first-order transition in 2D leading to a coexistence regime of pinned and unpinned areas. Our data demonstrate that the original concept of Aubry not only survives in 2D but is relevant for the design of nanoscopic machines and devices at ambient temperature.
- Received 20 November 2017
- Revised 1 February 2018
DOI:https://doi.org/10.1103/PhysRevX.8.011050
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Synopsis
Transition to Superlubricity in 2D
Published 28 March 2018
Studying particles sliding over a 2D potential lattice, researchers have observed a phase transition between a frictional regime and a frictionless, “superlubric” regime
See more in Physics
Popular Summary
Friction not only consumes substantial energy but also wears down materials as they move relative to one another. The possibility of frictionless motion has endless possibilities; wear and tear would be greatly reduced, and objects could be moved with minute forces. Physicist Serge Aubry proposed a way to achieve such frictionless, or “superlubric,” behavior over 40 years ago. Unfortunately, those predictions addressed a rather artificial situation: a one-dimensional array of a few particles sliding across a corrugated surface at zero temperature. Using experiments and simulations, we demonstrate that frictionless sliding can be achieved even under realistic conditions such as a two-dimensional extended contact at room temperature.
To visualize the motion of particles in real space and real time, we have studied a monolayer of micrometer-sized particles sliding on a corrugated surface. Our results reveal that a slight tilt in the orientation of the monolayer relative to the underlying surface produces frictionless sliding. When the contact strength between the surfaces is increased, there is a sharp transition from a fully superlubric state to a strongly pinned state where the particles become trapped in potential barriers. At intermediate contact strengths, we find a novel state where superlubric and strongly pinned areas coexist.
Our results demonstrate that Aubry’s original concept not only works in two dimensions but can also become relevant for the design of nanoscopic machines and devices at ambient temperatures.