Yu Zhaoyang, Huang Mengyuan, Zhang Xianren
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology 100029 Beijing China
Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf 01328 Dresden Germany
Nanoscale Adv. 2024 Jul 26;6(19):4922-31. doi: 10.1039/d4na00252k.
Amonton's law of friction states that the friction force is proportional to the normal force in magnitude, and the slope gives a constant friction coefficient. In this work, with molecular dynamics simulation, we study how the kinetic friction at the nanoscale deviates qualitatively from the relation. Our simulation demonstrates that the friction behavior between a nanoscale AFM tip and an elastic graphene surface is regulated by the coupling of the applied normal force and the substrate deformability. First, it is found that the normal load-induced substrate deformation could lower friction at low load while increasing it at high load. In addition, when the applied force exceeds a certain threshold another abrupt change in friction behavior is observed, , the stick-slip friction changes to the paired stick-slip friction. The unexpected change in friction behavior is then ascribed to the change of the microscopic contact states between the two surfaces: the increase in normal force and the substrate deformability together lead to a change in the energy landscape experienced by the tip. Finally, the Prandtl-Tomlinson model also validates that the change in friction behavior can be interpreted in terms of the energy landscape.
阿蒙顿摩擦定律指出，摩擦力在大小上与法向力成正比，斜率给出一个恒定的摩擦系数。在这项工作中，我们通过分子动力学模拟研究了纳米尺度下的动摩擦力如何在性质上偏离该关系。我们的模拟表明，纳米尺度原子力显微镜（AFM）探针与弹性石墨烯表面之间的摩擦行为受外加法向力与基底可变形性耦合的调节。首先，发现法向载荷引起的基底变形在低载荷时会降低摩擦力，而在高载荷时会增加摩擦力。此外，当外加力超过某个阈值时，会观察到摩擦行为的另一个突然变化，即，粘滑摩擦变为成对粘滑摩擦。摩擦行为的意外变化随后归因于两个表面之间微观接触状态的变化：法向力的增加和基底可变形性共同导致探针所经历的能量景观发生变化。最后，普朗特 - 汤姆林森模型也验证了摩擦行为的变化可以根据能量景观来解释。
