Two-dimensional Materials: A Wonderland for Tribology

Two-dimensional (2D) materials are materials consisting of a single or a few layers of atoms. Owing to their outstanding physical, mechanical and chemical properties, 2D materials such as graphene, hexagonal BN, and MoS2 have attracted extensive attention. Although their thickness is only a few atomic layers, they have excellent lubrication performance, showing a very low friction coefficient and wear rate, which gives them strong potential applications for improving the efficiency, durability and environmental compatibility of future mechanical systems.

Overview of structural, mechanical, electrical, thermal, and chemical properties of 2D materials that are relevant to tribological performance.

Dr. Qunyang Li, an Associate Professor in the Department of Engineering Mechanics at Tsinghua University together with his collaborators have recently published a review article, entitled “Tribology of two-dimensional materials: From mechanisms to modulating strategies”, in the journal Materials Today. This article reviews the most recent advances in tribological studies of 2D materials, with particular focus on the unique mechanisms underlying their novel friction and wear behavior. Based on fundamental understanding, the impacts of the atomic structures of shearing interfaces and environmental factors are summarized and various strategies for achieving friction modulation and superlubricity are discussed. The prospects for the practical applications of 2D materials in engineering mechanical systems are also presented.

Dr. Li's research group focuses on the physical and mechanical properties related to surface and interfaces. They have made great progress in revealing and understanding the fundamentals of friction. For example, together with their collaborators, they observed and explained the thickness-dependent frictional behavior that is universal for two-dimensional materials on weakly adherent substrates [Science, 328, 76-80 (2010)]; they directly confirmed the role of chemical bonding in the frictional ageing behavior of rock materials [Nature, 480, 233-236 (2011)]; they discovered the “negative” friction coefficient on chemically-modified graphite surface [Nature Materials, 11, 1032-1037 (2012)] and the robust ultra-low friction state of graphene via moiré superlattice confinement [Nature Communications, 7, 13204 (2016)]; they also revealed the unique contribution of contact quality on the frictional behavior of 2D materials [Nature, 539, 541-545 (2016)].

The review article is co-authored with Dr. Tianbao Ma, an Associate Professor of the State Key Laboratory of Tribology at Tsinghua University, Dr. Ali Erdemir, President of the International Tribology Council, and Mr. Shuai Zhang, a PhD student at Tsinghua University.

Materials Today is a flagship academic journal (impact factor: 24.5) covering the most innovative, cutting edge and influential work of broad interest to the materials science community.

Link to the review article:
https://www.sciencedirect.com/science/article/pii/S1369702118309039