Collaborative Research: Electrotunable and Curvature-Dependent Friction at Nanoscale Contacts Lubricated by Ionic Liquids

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Effective friction control is crucial in manufacturing processes: in macroscale manufacturing, minimizing friction helps lower costs; in micro-manufacturing and ultra-high precision manufacturing, friction control often determines the quality and functionalities of finished products. This project aims to explain how ionic liquids lubricate single-point contacts between dielectric and conducting surfaces, and to investigate how the friction can be tuned using electrical potential between the surfaces. The research will be conducted by integrating atomic force microscopy experiments and molecular modeling. The mechanistic insight gained in this project will help improve the design of new ionic liquid lubricants and additives. This progress will help improve the sustainability and efficiency of manufacturing processes and thus increase U.S. industrial productivity and competitiveness. Furthermore, the collaborative project will help develop the workforce in the US, broaden the participation of underrepresented groups in research, and positively impact engineering education and the dissemination of research to industry.This project will determine the relationship between surface curvature, surface potential, and friction at single-asperity contacts mediated by ionic liquids. Model systems consisting of atomic force microscopy tips and nanoparticle-decorated substrates coated with durable single-layer graphene will be adopted to quantify the effects of surface roughness and potential on lubrication. Rigorous molecular simulations, in which electrical potentials are imposed on conducting surfaces, will resolve ionic liquids' molecular structure and dynamics in nanoscale tribosystems to elucidate the mechanisms underlying electrotunable friction. Molecular modeling and atomic force microscopy experiments will be used in a complementary manner and at accessible length scales to enable the molecular understanding of friction. The fundamental insights on the modulation of lubrication by surface roughness and electrical potential at single-asperity contacts will provide the theoretical underpinning for understanding how tribological behaviors depend on choices of ionic liquids and surfaces.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.