Negative friction coefficient in microscale graphite/mica layered heterojunctions

Bingtong Liu; Jin Wang; Shuji Zhao; Cangyu Qu; Yuan Liu; Liran Ma; Zhihong Zhang; Kaihui Liu; Quanshui Zheng; Ming Ma

doi:10.1126/sciadv.aaz6787

Negative friction coefficient in microscale graphite/mica layered heterojunctions

Sci Adv. 2020 Apr 17;6(16):eaaz6787. doi: 10.1126/sciadv.aaz6787. eCollection 2020 Apr.

Authors

Bingtong Liu^{1

2}, Jin Wang^{3

4}, Shuji Zhao^{1

2

3}, Cangyu Qu^{3

4}, Yuan Liu^{1

2}, Liran Ma^{1

2}, Zhihong Zhang⁵, Kaihui Liu⁵, Quanshui Zheng^{1

3

4}, Ming Ma^{1

2

3}

Affiliations

¹ State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
² Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
³ Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
⁴ Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
⁵ State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China.

Abstract

The friction of a solid contact typically shows a positive dependence on normal load according to classic friction laws. A few exceptions were recently observed for nanoscale single-asperity contacts. Here, we report the experimental observation of negative friction coefficient in microscale monocrystalline heterojunctions at different temperatures. The results for the interface between graphite and muscovite mica heterojunction demonstrate a robust negative friction coefficient both in loading and unloading processes. Molecular dynamics simulations reveal that the underlying mechanism is a synergetic and nontrivial redistribution of water molecules at the interface, leading to larger density and more ordered structure of the confined subnanometer-thick water film. Our results are expected to be applicable to other hydrophilic van der Waals heterojunctions.

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