Exploring the Physical Limits of Structural Superlubricity

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This grant will focus on “structural superlubricity”, a peculiar phenomenon where friction between two objects nearly vanishes, without the use of any lubricants. Friction is the leading cause of useful energy loss in mechanical systems and processes, with an enormous impact on national energy demand. In fact, recent estimates indicate that economic losses associated with friction can amount up to a few percent of the gross domestic product of a developed nation such as the USA. New methods devised to mitigate friction have important implications for the conservation of useful energy, as well as economic and environmental sustainability. Structural superlubricity is one such method, which has been recently experimentally demonstrated for microscopic contacts. This research project will explore the physical limits of structural superlubricity in terms of speed of motion, operation temperature, and contact size, to determine if the idea can be employed to establish ultra-low friction sliding in mechanical systems of practical relevance. The project has a significant diversity component, as it will be conducted at UC Merced, a Hispanic Serving Institution where many students are first-generation. The research efforts will be additionally complemented by outreach activities aimed at K-12 students in the socio-economically underserved region of San Joaquin Valley. The overarching objective of the project is to form a fundamental understanding of the physical limits of structural superlubricity, in terms of its robustness against changes in operating conditions such as temperature and sliding speed, as well as the length scale up to which the ultra-low friction state can be preserved. To achieve this objective, manipulation experiments based on atomic force microscopy will be performed, whereby gold flakes will be laterally moved on top of atomically flat graphite substrates and the associated friction forces will be recorded with high precision. Experiments will be performed at different temperatures, sliding speeds, and on flakes of sizes approaching the micrometer regime. The obtained results will provide crucial experimental data for the still nascent theories about the physical limitations of structural superlubricity.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.