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

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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.