Low friction and rotational dynamics of crystalline flakes in solid lubrication

¹ Radboud University Nijmegen, Institute for Molecules and Materials - Heyendaalseweg 135, 6525AJ Nijmegen, the Netherlands, EU
² Donetsk Institute for Physics and Engineering of NASU - 83144, Donetsk, Ukraine
³ School of Chemistry, Tel Aviv University - 69978 Tel Aviv, Israel

^a A.S.deWijn@science.ru.nl

Received: 5 May 2011
Accepted: 29 July 2011

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.