CAREER: Linking Molecular Structure and Lubrication Mechanism in Halogen-Free, Boron-Based Ionic Liquids

学院早期职业发展(Career)计划拨款支持对离子液体(ILS)的基础研究，离子液体是一种成分可调、熔点低于100°C的盐。由于其独特的性质和良好的润滑性能，离子液体是绿色制造方法中用于切削液的有前途的添加剂。ILS用于润滑的一个关键挑战是缺乏对ILS分子结构和润滑性能之间关系的了解。这笔赠款支持旨在填补这一知识空白的基础研究，方法是确定一类在摩擦学上有希望的ILS的润滑机理(S)，即无卤基、硼基ILS(HF-BILs)，并在它们的分子结构和摩擦学性能之间建立联系。该项目产生的新知识使ILS能够合理地设计具有增强润滑性能的ILS，这将有助于通过改善机械加工过程的可持续性和效率来提高美国的工业生产率和竞争力。与该项目的研究目标相辅相成的是教育项目，该项目将增加退伍军人参加STEM项目，并与小学教师合作，增加K-5学生接触科学和工程的机会。研究项目解决了ILS用于润滑目的的两个主要公开问题：a)ILS的润滑性能与ILS化学的相关性；b)ILS在滑动界面上的应力诱导、热激活反应、所产生的表面反应层的化学/结构以及ILS分子结构之间的相互关系。这项研究涉及合成具有系统不同组成的离子液体，这些离子液体用于原子力显微镜原位实验，该实验涉及定义明确的单一粗糙度滑动接触。该实验框架验证了滑动界面牺牲低剪切强度层的生长速率随正常应力和温度呈指数增加的假设，但受IL分子结构的显著影响。反应层的化学和纳米机械性能的非原位表征揭示了HF-BILs中的化学变化、滑动界面上的化学反应活性和摩擦学诱导的反应层的性质之间的相互关系。这项研究的结果有助于在先进制造方法的下一代润滑剂中实现具有增强摩擦学性能的ILS的预测性设计、开发和实施。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。

This Faculty Early Career Development (CAREER) Program grant supports fundamental research on ionic liquids (ILs), which are salts with tunable composition and melting point below 100ºC. Owing to their unique properties and good lubrication performance, ILs are promising additives for cutting fluids used in green manufacturing approaches. A critical challenge in the use of ILs for lubrication purposes is the lack of understanding of the relationship between IL molecular structure and lubrication performance. This grant supports fundamental research aiming to fill this knowledge gap by identifying the lubrication mechanism(s) of a class of tribologically-promising ILs, namely halogen-free, boron-based ILs (hf-BILs), and establishing links between their molecular architecture and tribological properties. The new knowledge emerging from the project enables the rational design of ILs with enhanced lubrication performance, which will contribute to increasing the U.S. industrial productivity and competitiveness by improving the sustainability and efficiency of machining processes. Complementary to the research goal of this project are the educational programs which will increase the inclusion of veterans in STEM programs and collaborate with elementary school teachers to increase the exposure of K-5 students to science and engineering.The research project addresses two major open questions in the use of ILs for lubrication purposes: a) the dependence of the lubrication performance of ILs on the IL chemistry; b) the interrelationship between the stress-induced, thermally-activated reactions of ILs at sliding interfaces, the chemistry/structure of the resulting surface reaction layers, and IL molecular structure. The study involves the synthesis of ILs with systematically varied composition, which are used in in situ atomic force microscopy experiments involving well-defined, single asperity sliding contacts. This experimental framework tests the hypothesis that the growth rate of sacrificial, low-shear-strength layers at sliding interfaces increases exponentially with normal stress and temperature but is significantly affected by the IL molecular structure. The ex situ characterization of the chemistry and nanomechanical properties of the reaction layers shed light on the interrelationship between chemical changes in hf-BILs, their chemical reactivity at sliding interfaces, and properties of the tribologically-induced reaction layers. The findings of this study are instrumental in enabling the predictive design, development, and implementation of ILs with enhanced tribological properties in next-generation lubricants for advanced manufacturing methods.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.