Collaborative Research: Understanding the Lubrication Mechanisms of Environmentally-Compatible Protic Ionic Liquids

人们对工程系统和功能材料的需求越来越大，通过改善摩擦、磨损和润滑性能(也称为摩擦学性能)来提高能效和更长的寿命。这种需求是由经济和社会需求驱动的，例如最大限度地减少温室气体排放，确保能源安全，以及提高工业产出和竞争力。离子液体(ILS)是组成可调、熔点低于100°C的熔盐，其物理和化学性质使其成为很有前途的润滑液。然而，普通离子液体的高成本和腐蚀性，以及对离子液体分子结构与润滑性能之间关系的认识不足，限制了离子液体在摩擦学应用中的大规模应用。一种低成本、环保、无腐蚀性的质子型离子液体(PILs)--胆碱氨基酸质子型离子液体(PILs)--已成为这些常见离子液体的可能替代品。本项目旨在了解PIL分子结构如何影响它们在固体滑动界面上的排列和反应。该项目还将利用德克萨斯大学奥斯汀分校(UT-Austin)和罗彻斯特理工学院(RIT)的主要研究人员的互补专业知识和资源，通过为来自不同背景和STEM中代表性不足的群体的本科生和研究生提供培训和教育机会，提高美国工程劳动力的质量、规模和多样性。研究项目将确定胆碱氨基酸柱-一类无卤素、环保的柱-的分子结构与其功能性能(即纳米级和大规模润滑行为)之间的联系。这项研究还将研究固体/桩界面上发生的界面过程如何响应空间限制和施加的法向压力和剪切力而产生功能行为。工作假设是，包括表面吸附、界面相变和剪切诱导的机械力化学反应在内的多种界面过程是胆碱氨基酸柱良好的润滑性能的基础；此外，这些过程的动力学可以通过调整离子的分子结构(例如，烷基链的长度)来控制。该团队的互补专业知识和仪器将被应用于合成具有系统变化的结构的PILS。这些PILs将被用于纳米和宏观摩擦学实验，以验证工作假说。项目成果将用于设计具有改进的和特定于任务的摩擦学特性的新型ILS。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

There is growing demand for engineering systems and functional materials with improved energy efficiency and longer lifetime through improved friction, wear, and lubrication performance, also known as tribological performance. This demand is driven by economic and societal needs such as minimizing greenhouse gas emissions, ensuring energy security, and improving industrial output and competitiveness. Ionic liquids (ILs) are molten salts with tunable composition and melting points below 100ºC. Their physical and chemical properties make them promising lubricating fluids. However, the high cost and corrosiveness of common ILs combined with a poor understanding of the relationship between IL molecular structure and lubrication performance has limited large-scale utilization of ILs in tribological applications. A class of low-cost, eco-friendly, non-corrosive protic ionic liquids (PILs) called choline amino acid PILs has emerged as a possible alternative to these common ILs. This project seeks to understand how PIL molecular structures affect their arrangement and reaction at solid sliding interfaces. The project will also leverage the complementary expertise and resources of the principal investigators at the University of Texas-Austin (UT-Austin) and Rochester Institute of Technology (RIT) to enhance the quality, size, and diversity of the US engineering workforce through training and education opportunities for undergraduate and graduate students from diverse backgrounds and underrepresented groups in STEM.The research project will identify links between the molecular structure of choline amino acid PILs – a class of halogen-free, eco-friendly PILs – and their functional performance (i.e., nanoscale and macroscale lubricating behavior). The research will also examine how the functional behavior emerges from the interfacial processes occurring at solid/PILs interfaces in response to spatial confinement and applied normal pressure and shear forces. The working hypothesis is that multiple interfacial processes, including surface adsorption, interfacial phase transformation, and shear-induced mechano-chemical reaction, underpin the promising lubricating properties of choline amino acid PILs; in addition, the kinetics of these processes can be controlled by tailoring the molecular structure of the ions (e.g., length of the alkyl chains). The team’s complementary expertise and instrumentation will be applied to synthesize PILs with systematically-varied structures. These PILs will be employed in nanoscale and macroscale tribological experiments to test the working hypothesis. The project outcomes will inform the design of novel ILs with improved and task-specific tribological properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.