基于界面力-化学反应的石墨烯薄膜磨损自修复机制研究

Graphene, due to its excellent mechanical, electrical, thermal and optical properties, is recognized as the greatest “magic material” in the 21 century. Because of its ultra-high mechanical strength, easy shear capability between interlayers, and ultra-thin thickness to a few layers of atoms, graphene stood out in the efforts of seeking new material for solid lubrication. However, there still have some hard problems to overcome when use graphene as a realistic solid lubricant. For example, graphene tends to wore easily, and the tribological performance of graphene is sensitively dependent on the testing environment. Environment molecules tend to absorb on the rubbing surface, and play their important role in the wear and failure process of graphene. Therefore, the understanding and control of behavior of small molecules on the rubbing surface is a very important step to improve the tribological performance of graphene and to advance its realistic application. In this project, the first-principles calculation, reactive molecular dynamics simulation and experimental methods will be used. We will study the relationship between the physical and chemical behavior of environment molecules at the microscale and the tribological performance of graphene at the macroscale, with the purpose to reveal the effects of environmental gas on the tribological performance and wear mechanisms of graphene. Furthermore, we will seek out a proper matching of carbon source molecules, substrate materials and metal catalytic atoms, which can facilitate carbon source molecules to react with defective parts of graphene. A self-healing mechanism based on this mechanochemical reaction on frictional interface will be proposed to control the wear behavior of graphene. This research will further promote the realistic application of graphene sheets and other two-dimensional materials be used as solid lubricants.

石墨烯具有力学、电学、热学和光学等诸多方面的优异特性，堪称21世纪最伟大的“传奇材料”。由于其超高强度、易于剪切的层间界面，且超薄至几个原子层的厚度，使石墨烯作为潜在的固体润滑新材料而脱颖而出。但距离其实际应用，尚存在石墨烯易于磨损、摩擦磨损性能敏感地依赖于环境气氛等问题。环境分子极易吸附、并参与到石墨烯薄膜的摩擦磨损过程中，理解和控制摩擦界面的分子尺度行为以增强其摩擦学性能，成为石墨烯实现实际应用的关键。本项目拟采用第一性原理计算、反应力场分子模拟，并结合实验方法，研究摩擦界面环境分子的物理化学行为与摩擦学性能之间的关系，揭示环境气氛对石墨烯摩擦磨损特性的影响与作用机制。进而，通过适当配伍碳源分子、基底材料和金属催化原子，促使碳源分子与缺陷石墨烯间的力-化学反应，提出基于摩擦界面力-化学反应的石墨烯自修复机制和方法。将为促进石墨烯薄膜、二维材料作为固体润滑剂的实际应用提供理论与实验支持。

本项目针对石墨烯作为润滑材料存在易于磨损、摩擦学性能敏感地依赖于环境气氛等问题，围绕石墨烯薄膜的磨损特性、环境分子的作用机制，以及通过适当条件下石墨烯薄膜的自修复行为抑制其磨损失效过程等开展研究，取得了一些重要的研究成果：(1)应用反应力场分子动力学模拟，研究了界面相互作用、石墨烯结构缺陷、基底材料化学（镍、铂和铜基底）等对石墨烯薄膜摩擦学性能的影响，揭示了石墨烯薄膜易磨损特性的分子尺度机制，发现了与对偶表面或基底表面形成化学键、以及磨损过程中的反应级联效应对石墨烯薄膜抗磨性的显著削弱作用。(2)研究了在不同环境粒子（氢原子、CHx(x=1,2,3)离子等）氛围下石墨烯薄膜的磨损失效过程，揭示了环境粒子在磨损石墨烯表面的吸附行为，提出了环境粒子吸附对石墨烯磨损过程产生影响的多种作用机制，即吸附在磨损空洞两侧拉伸应力区域或碳链上的环境粒子，通过改变磨损空洞扩展方向或促使碳链断裂，可能显著地影响石墨烯薄膜的磨损失效过程。(3)研究了在碳原子辐射或金属原子（镍、铂原子）催化作用下缺陷石墨烯的修复过程，分析了系统温度、碳原子入射能量、金属催化原子对石墨烯修复过程的影响，提出了可获得良好修复效果的较高温度（≥1600K）与适当入射能量相匹配的修复条件，揭示了金属原子的催化作用机制，即对修复过程中易形成缺陷结构的转变作用，以及在石墨烯薄膜上的迁移能力决定了金属原子的催化修复效果。通过本项目研究，在Tribology International、Tribology Letters、Applied Surface Science、Langmuir和《物理学报》等国内外重要学术期刊发表SCI收录论文14篇，其中JCR一区5篇、二区4篇。两名项目参与人获重庆大学优秀硕士学位论文。