Collaborative Research: Friction on 2D Materials -- Understanding the Critical Role of Edge Chemistry

合作研究：二维材料上的摩擦——了解边缘化学的关键作用

基本信息

批准号：
1727571
负责人：
Seong Kim
金额：
$ 31.9万
依托单位：
Pennsylvania State Univ University Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2020-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1727571&HistoricalAwards=false
关键词：
Collaborative Research Friction 2D Materials

项目摘要

Two-dimensional layered materials play important roles in a variety of applications, one of which is as a solid lubricant that minimizes friction and wear. Many two-dimensional layered materials exhibit ultra-low friction only under the "proper" environmental conditions, and the ideal environment may vary from material to material. One explanation for this environmental sensitivity comes from the fact that two-dimensional materials have not only the slippery topmost surface, but also surface step edges where the topmost layer starts or stops. Such surface sites may react chemically with molecules in the environment, like water and hydrocarbons, which will in turn affect friction. This project develops a fundamental understanding of the critical role of the ubiquitous step edges and their reactions with environmental gases in determining friction of two-dimensional materials. This basic research on surface chemistry can lead to new classes of lubricants and impact other applications, such as advanced electronics, where the edge of the 2D materials play a strong role.The common feature of two-dimensional materials is atomically-flat layers with weak inter-lamellar interactions, leading to low shear resistance between layers, which has long been believed to be the origin of super-lubricity. This simple picture does not explain lubrication failure of graphite in vacuum, poor performance of molybdenum disulfide in humid air, and poor lubricity of boric acid in dry air. The work is based on the premise that geometrically-flat lamellae are necessary for super-lubricity, but not sufficient; attaining ultra-low friction requires both the low-corrugation potential surface of the basal plane and proper passivation of edge sites of the basal plane. This hypothesis will be tested through judicious experimental design and state-of-the-art surface analysis methods as well as molecular dynamics simulations that can model chemical reactions at sliding interfaces. This research will address the following key questions: (i) what is the intrinsic reason that friction of two-dimensional layered materials is sensitive to humidity in the environment and why do different materials exhibit very different humidity dependence; (ii) what is the molecular origin of the frictional response of graphite step edges; and (iii) what are the factors governing interface fracture and inter-lamellar slip of two-dimensional materials in various environments. The grant supports a researcher exchange program between two institutions emphasizing the engagement of underrepresented groups.

二维层状材料在各种应用中发挥着重要作用，其中之一是作为固体润滑剂，最大限度地减少摩擦和磨损。许多二维层状材料只有在“适当”的环境条件下才会表现出超低摩擦，而理想的环境可能因材料而异。对这种环境敏感性的一种解释来自这样的事实：二维材料不仅具有光滑的最顶层表面，而且还具有最顶层开始或停止的表面台阶边缘。这些表面位点可能会与环境中的分子（例如水和碳氢化合物）发生化学反应，进而影响摩擦。该项目对普遍存在的阶梯边缘及其与环境气体的反应在确定二维材料摩擦方面的关键作用有了基本的了解。这项关于表面化学的基础研究可以催生新型润滑剂并影响其他应用，例如先进电子学，其中二维材料的边缘发挥着重要作用。二维材料的共同特征是原子级平坦的层，具有弱层间相互作用，导致层间剪切阻力低，长期以来人们认为这是超润滑性的起源。这个简单的图并不能解释石墨在真空中润滑失效、二硫化钼在潮湿空气中性能差以及硼酸在干燥空气中润滑性差。这项工作的前提是几何平坦的薄片对于超润滑性是必要的，但还不够。获得超低摩擦需要基面的低波纹势表面和基面边缘部位的适当钝化。这一假设将通过明智的实验设计和最先进的表面分析方法以及可以模拟滑动界面化学反应的分子动力学模拟来检验。本研究将解决以下关键问题：（i）二维层状材料的摩擦对环境湿度敏感的内在原因是什么，以及为什么不同的材料表现出截然不同的湿度依赖性； (ii) 石墨台阶边缘摩擦响应的分子起源是什么； (iii) 影响二维材料在不同环境下界面断裂和层间滑移的因素有哪些。该赠款支持两个机构之间的研究人员交流计划，强调代表性不足群体的参与。