Collaborative Research: Quantitative Prediction of Sliding Friction Using Integrated Theory and Experiments

本研究旨在对模型边界膜的能量耗散、界面结构和摩擦特性有一个定量的认识。虽然到目前为止，理论方法能够对滑动摩擦提供定性的见解，但它们还不能定量地描述滑动界面的结构和相关的摩擦力。这项研究的方法将是将在超高真空中对由金属衬底上的一系列等结构碱卤化物组成的明确模型边界膜进行的实验与使用定制的高精度相互作用势的分子动力学模拟相结合，该相互作用势是从相同系统的密度泛函计算中获得的。如果成功，这项研究的好处将包括了解润滑剂添加剂或气相润滑剂在滑动的固体-固体界面上发生化学反应形成的边界膜的摩擦特性。这一基本认识将支撑设计有效润滑剂的努力，这种润滑剂能形成低摩擦或低磨损的薄膜，从而节省能源，延长机器寿命，并使美国受益？经济舱。此外，理解滑动摩擦是一项独特的实验挑战，因为这一过程发生在无法接触的滑动固体-固体界面上，不能直接询问。这意味着在理解这种界面方面的进步将依赖于在相同系统上进行的实验和理论方法的整合。能够为本提案中探讨的简单系统实现这一点，将为理解更复杂的滑动界面开发理论和实验策略。最后，综合实验和理论方法将为学生提供广泛的教育，并将涉及本科生和代表性不足的少数群体。在过去的几十年里，理论方法的发展和实验方法的改进已经导致了进行科学的方式的根本转变，这将需要理论和实验相结合的研究生和本科生教育。这一点在最近一期《摩擦学快报》特刊中得到了强调，该特刊由该提案的主要研究人员共同编辑，题为《通过综合模拟和实验取得摩擦学进展》。

This research is about obtaining a quantitative understanding of energy dissipation, interfacial structure and friction of model boundary films. While theoretical methods have hitherto been able to provide qualitative insights into sliding friction, they have not yet been able to quantitatively describe the structure of a sliding interface and the associated friction forces. The approach of this research will be to combine experiments in ultrahigh vacuum on well-defined model boundary films consisting of a range of isostructural alkali halides on metal substrates with molecular dynamics simulations using tailored, high-precision interaction potentials obtained from density function theory calculations of the same systems. If successful, the benefits of this research will include an understanding of the friction properties of the boundary films that are formed by chemical reactions between lubricant additives or gas-phase lubricants at a sliding, solid-solid interface. This fundamental understanding will underpin efforts to design effective lubricants that form films with low friction or wear, thereby resulting in energy savings and longer machine lifetimes, and benefit the United States? economy. In addition, understanding sliding friction poses a unique experimental challenge because the processes occur at an inaccessible, sliding solid-solid interface that cannot be interrogated directly. This means that advances in understanding such interfaces will rely on integrating experiments and theoretical methods carried out on the same systems. Being able to achieve this for the simple systems explored in this proposal will develop the theoretical and experimental strategies for understanding more complex sliding interfaces. Finally, the integrated experimental and theoretical approaches will provide a broad-based education for students and will involve both undergraduates and under-represented minorities. Developments in theoretical methods and the refinement of experimental approaches over the past few decades have resulted in a fundamental shift in the way that science is carried out and will require both graduate and undergraduate education that integrates theory and experiment. This has been emphasized in a recent special issue of Tribology Letters co-edited by the Principal Investigators of this proposal entitled ?Progress in Tribology Through Integrated Simulations and Experiments?.