npj Computational Materials

Mechanism of contact pressure-induced friction at the amorphous carbon/alpha olefin interface (无定形碳/α烯烃界面处因接触压力引起的摩擦机理)
Xiaowei Li, Aiying Wang & Kwang-Ryeol Lee
npj Computational Materials 4:53 (2018)
doi:s41524-018-0111-x
Published online:26 September 2018
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摘要:将无定形碳（a-C）膜与润滑油组合可以显着改善移动机械部件的摩擦性能和寿命。然而，暴露于高接触压力时，由于缺乏界面结构的有关信息，因此不能很好地了解摩擦机理。本研究选择线性α-烯烃（C5H10）作为润滑剂，并通过反应分子动力学模拟，研究接触压力下a-C / C5H10 / a-C滑动界面结构的演变。我们的结果表明，与无润滑剂相比，将C5H10引入a-C / a-C界面可使摩擦系数降低多达93％，尽管润滑效率很大程度上取决于接触压力。特别地，增加接触压力不仅引起润滑剂与α-C的结合，还促进C5H10碳-碳骨架经特定的断裂而解离，这决定了摩擦行为。本研究结果揭示了潜在的润滑机理，并据此可开发新型长寿命有效润滑系统。　　

Abstract:Combining an amorphous carbon (a-C) film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components. However, the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure.Here, we select linear alpha olefin, C5H10, as a lubricant and study the evolution of the structure of the a-C/C5H10/a-C sliding interface under contact pressure via reactive molecular dynamics simulation.Our results suggest that introducing C5H10 into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant, although the lubricating efficiency strongly depends on the contact pressure.In particular, increasing the contact pressure not only induces the binding of the lubricant with a-C, but also facilitates the dissociation of the C5H10 carbon-carbon skeleton by specific scissions, which governs the friction behavior.These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes.

Editorial Summary

Friction: pressure key to lubrication (摩擦：把重点对准润滑机理)

将无定形碳膜与润滑油结合虽可改善摩擦性能，但它还是取决于接触压力。来自韩国科学技术研究院的Xiaowei Li和Kwang-Ryeol Lee领导的团队，利用分子动力学模拟研究了两种无定形碳膜与润滑剂烯烃油之间的摩擦。令人惊讶的是，在两个表面在滑动期间，增加压力会导致摩擦减小，接触压力继续增大，摩擦又会增加。这是由于压力增加使油分子分离，其中的碎片重新与无定形碳表面组合，使它们钝化。然而，在高压下表面的钝化在降低摩擦方面，不如在中等压力下油流体动力润滑那样有效。了解压力和油在摩擦中的作用可以帮助指导我们改进润滑剂的设计。

While combining an amorphous carbon film with lubricating oil can improve friction performance, it depends on contact pressure. A team led by Xiaowei Li and Kwang-Ryeol Lee from the Korea Institute of Science and Technology used molecular dynamics simulations to investigate the friction of two amorphous carbon films with olefin oil as lubricant.Surprisingly, increasing pressure during sliding caused a decrease followed by an increase in the friction between the two surfaces. This was due to increasing pressure dissociating the oil molecules, fragments of which recombined with the amorphous carbon surfaces to passivate them.Passivation of the surfaces at high pressures, however, was not as efficient at reducing friction as hydrodynamic lubrication from the oil at medium pressures.Understanding the role of pressure and oils in friction can help guide our design of improved lubricants.