Liu Bingtong, Wang Jin, Zhao Shuji, Qu Cangyu, Liu Yuan, Ma Liran, Zhang Zhihong, Liu Kaihui, Zheng Quanshui, Ma Ming
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Sci Adv. 2020 Apr 17;6(16):eaaz6787. doi: 10.1126/sciadv.aaz6787. eCollection 2020 Apr.
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.
根据经典摩擦定律，固体接触的摩擦力通常表现出对法向载荷的正相关性。最近在纳米级单粗糙接触中观察到了一些例外情况。在此，我们报告了在不同温度下微尺度单晶异质结中负摩擦系数的实验观察结果。石墨与白云母云母异质结界面的结果表明，在加载和卸载过程中都存在稳健的负摩擦系数。分子动力学模拟表明，其潜在机制是界面处水分子的协同且非平凡的重新分布，导致受限的亚纳米厚水膜具有更大的密度和更有序的结构。我们的结果有望应用于其他亲水性范德华异质结。
