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

运动部件的润滑对于减少机械部件的摩擦和磨损至关重要。典型的润滑剂是含有减摩添加剂的碳氢化合物。提高润滑过程的效率及其使用寿命都可以减少能源消耗、降低维护成本并减少废润滑油的量。然而，润滑剂可能会因使用过程中的加热（会破坏润滑剂结构）和轴承表面发生的化学反应而磨损。该奖项支持通过涉及过程实验研究及其模拟的协作努力，研究导致基本润滑剂化学分解的基本机制。对这些在典型使用条件下发生的与表面相关的化学反应缺乏基本了解。 这些化学反应的测定可用于设计新的更具弹性的润滑剂，其中这些有害反应被减少或消除，从而改进润滑剂。因此，研究结果将使依赖润滑的美国经济和技术的许多部门受益。润滑技术的改进将延长机械系统的使用寿命并降低能耗。加州大学默塞德分校和威斯康星大学密尔沃基分校积极让本科生参与这些研究活动，其中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。实验将在由气相二烷基二硫化物润滑的清洁铜和金组成的简单模型系统上进行，该系统虽然简单，但保留了实际润滑剂的关键方面。反应路径及其动力学将使用原位技术进行测量，通过监测超高真空（UHV）中滑动产生的气相产物，并测量摩擦力的演变。这些实验将通过同一设备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，该模拟使用反应电位，可以揭示有助于提高滑动界面反应速率的关键成分。从分子动力学模拟和特高压实验中获得的见解将用于开发准确的分析模型。这些综合实验、模拟和分析模型将带来对最终构成润滑剂功能的摩擦化学反应中发生的基本步骤的新的基本理解。项目学生将通过院校之间的交流参与计算和实验两个方面。这些交流将提供独特的培训，并在计算和实验研究之间建立紧密的联系。

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.