Wen Xiangli, Bai Pengpeng, Li Yuanzhe, Cao Hui, Li Shaowei, Wang Bin, Fang Jingbo, Meng Yonggang, Ma Liran, Tian Yu
State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Langmuir. 2021 Mar 30;37(12):3628-3636. doi: 10.1021/acs.langmuir.0c03607. Epub 2021 Mar 18.
Liquid superlubricity results in a near-frictionless lubrication state, which can greatly reduce friction and wear under aqueous conditions. However, during the running-in process, a large number of abrasive particles are generated, and because these may lead to a breakdown in superlubricity performance, they should be effectively removed. In this paper, the morphology, size, and composition of abrasive particles were verified using scanning electron microscopy with energy-dispersive X-ray spectroscopy, and their influence on liquid superlubricity was explored through friction tests. Subsequently, different solvents were used to remove the abrasive particles, and the optimal cleaning process was determined by macroscopic tribo-tests and microscopic analysis. Finally, droplet-spreading experiments and a force-curve analysis were carried out to understand the abrasive-particle removal mechanism by different solvents. We found that SiO was the main component in the abrasive particles, and micron-sized SiO particles resulted in random "wave peaks" in the coefficient of friction and, thus, the superlubricity. Absolute ethanol + ultrapure water was determined to be the optimal solvent for effectively removing abrasive particles from friction-pair surfaces and helped the lubricant in exhibiting an ultralow friction coefficient for long periods of time. We proposed a "wedge" and "wrap" model to explain the abrasive-particle removal mechanism of different solvents. The SiO removal mechanism outlined in this study can be applied under aqueous conditions to improve the stability and durability of liquid superlubricity in practical engineering applications.
液体超润滑性会导致近乎无摩擦的润滑状态，这可以在水性条件下极大地降低摩擦和磨损。然而，在磨合过程中会产生大量磨粒，由于这些磨粒可能导致超润滑性能失效，因此应有效去除它们。本文利用扫描电子显微镜和能谱仪对磨粒的形貌、尺寸和成分进行了验证，并通过摩擦试验探究了它们对液体超润滑性的影响。随后，使用不同的溶剂去除磨粒，并通过宏观摩擦试验和微观分析确定了最佳清洗工艺。最后，进行了液滴铺展实验和力曲线分析，以了解不同溶剂去除磨粒的机制。我们发现SiO是磨粒中的主要成分，微米级的SiO颗粒导致摩擦系数出现随机的“波峰”，进而影响超润滑性。已确定无水乙醇+超纯水是从摩擦副表面有效去除磨粒的最佳溶剂，并且有助于润滑剂长时间呈现超低摩擦系数。我们提出了一个“楔入”和“包裹”模型来解释不同溶剂去除磨粒的机制。本研究中概述的SiO去除机制可应用于水性条件下，以提高液体超润滑性在实际工程应用中的稳定性和耐久性。
