Collaborative Research: Pushing Molecules Around: Identifying and Understanding the Elementary Steps in Tribochemical Reactions

为了减少机械部件的摩擦磨损，运动部件的润滑是必不可少的。典型的润滑剂是含有减摩添加剂的碳氢化合物。无论是提高润滑过程的效率，还是提高其使用寿命，都可以降低能源消耗、降低维护成本、减少润滑油废用量。然而，润滑油可能会因使用过程中的加热和轴承表面发生的化学反应而磨损，这可能会破坏润滑油的结构。该奖项支持对导致基本润滑剂化学分解的基本机理的研究，通过合作努力，包括工艺的实验研究和模拟。对于这些与表面有关的化学反应，在典型的使用条件下发生，缺乏基本的了解。这些化学反应的测定可用于设计新的更有弹性的润滑剂，减少或消除这些有害反应，从而改进润滑剂。因此，这项研究的结果将使依赖润滑油的美国经济和技术的许多部门受益。改进的润滑技术将延长机械系统的使用寿命，降低能源消耗。加州大学默塞德分校和威斯康星大学密尔沃基分校积极地让本科生参与这些研究活动，加州大学默塞德分校拥有很高比例的西班牙裔和第一代学生。实验将在简单的模型系统上进行，该系统由由气相二烷基二硫化物润滑的清洁铜和金组成，虽然简单，但仍保留了现实润滑剂的关键方面。通过监测超高真空(UHV)中滑动产生的气相产物，以及测量摩擦力的演变，将使用原位技术测量反应路径及其动力学。这些实验将由同一装置中摩擦区域的表面分析来补充。实验测量的动力学将使用分子动力学(MD)模拟进行建模，使用反应势可以揭示导致滑动界面上反应速度加快的关键成分。从MD模拟和超高压实验中获得的见解将被用来开发准确的分析模型。这些综合的实验、模拟和分析模型将导致对摩擦化学反应中发生的基本步骤的新的基本理解，这些基本步骤最终奠定了润滑油功能的基础。该项目的学生将通过院校之间的交流，参与计算和实验这两个方面。这些交流将提供独特的培训，并在计算研究和实验研究之间建立紧密联系。

Lubrication of moving parts is essential to reduce friction and wear of mechanical components. Typical lubricants are hydrocarbon compounds with friction-reducing additives. Both improving the efficiency of the lubrication process and its useful lifetime can reduce energy consumption, reduce maintenance costs, and reduce the amount of waste lubricant. Lubricants can, however, wear out through both the heating during use which can breakdown the lubricant structure and by chemical reactions occurring at the bearing surfaces. This award supports research into the basic mechanisms leading to this chemical breakdown of essential lubricants through a collaborative effort involving both experiment investigation of the process and its simulation. Fundamental understanding of these surface-related chemical reactions, occurring under conditions typical of their use, is lacking. The determination of these chemical reactions can be used to design new more resilient lubricants where these detrimental reactions are reduced or eliminated leading to improved lubricants. The results of the research will therefore benefit many sectors of the US economy and technology dependent on lubrication. Increased lifetime of mechanical systems and reduced energy consumption would result from improved lubrication technologies. The University of California-Merced and the University of Wisconsin-Milwaukee actively engage undergraduates into these research activities, with UC Merced possessing a high percentage of Hispanic and first generation students. Experiments will be carried out on simple model systems comprising clean copper and gold lubricated by gas-phase dialkyl disulfides, which, although simple, nevertheless retain the key aspects of realistic lubricants. The reaction pathways and their kinetics will be measured using in-situ techniques, by monitoring the gas-phase products produced by sliding in ultrahigh vacuum (UHV), and by measuring the evolution in friction force. These experiments will be complemented by surface analyses of the rubbed region in the same apparatus. The experimentally-measured kinetics will be modeled using molecular dynamics (MD) simulations using reactive potentials that can reveal the key ingredients contributing to increased reaction rates at a sliding interface. The insights obtained from the MD simulations and UHV experiments will be used to develop accurate analytical models. These integrated experiments, simulations and analytical models will lead to new fundamental understanding of the elementary steps that occur in tribochemical reactions that ultimately underlie lubricant function. The students within the program will participate in both aspects, calculation and experiment, through exchanges between the institutions. These exchanges will provide unique training and create a tight linkage between the computational and experimental studies.