Low friction and rotational dynamics of crystalline flakes in solid lubrication

TL;DR

This paper investigates how graphene flakes in solid lubrication maintain low friction through rotational dynamics, showing stable superlubric sliding even with randomly oriented patches, and identifies conditions for low friction states.

Contribution

It demonstrates that rotating graphene flakes can sustain superlubricity in solid lubrication, even with random orientations, and explores the effects of temperature and commensurability.

Findings

Stable superlubric sliding occurs with rotating graphene flakes.

Randomly oriented patches do not destroy superlubricity.

Low friction states are maintained at low temperatures for commensurate surfaces.

Abstract

Solids at incommensurate contact display low-friction, 'superlubric', sliding. For graphene flakes on a graphite surface, superlubric sliding is only temporary due to rotation of the flakes from incommensurate to commensurate contact with the substrate. We examine this rotational channel of friction in a prototype geometry of meso- and macroscopic solid lubrication. By molecular dynamics simulations and theoretical arguments we find that two surfaces lubricated by mobile, rotating graphene flakes exhibit stable superlubric sliding as for ideally incommensurate contacts also when they are covered by randomly oriented pinned graphene patches. For commensurate surfaces, we find a low friction state at low temperature where incommensurate states are not destroyed by thermal fluctuations.