Understanding Mechanical Activation of Chemical Reactions on Surfaces

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The development of advanced materials is essential for manufacturing new products and for economic and national security, with applications across multiple industrial sectors including defense, energy, transportation, aerospace, and healthcare. Machines made from these new materials will require lubricants to lower friction and mitigate wear that are tailored to the specific material. New lubricants are often designed by trial and error, which can be a long and uncertain process. Unfortunately, little is understood of the fundamental chemical processes occurring at a sliding interface that lead to formation of friction and/or wear reducing films. The goal of this work is to exploit an array of surface analytical tools and novel theoretical approaches to obtain fundamental insights into the way that forces acting on the surface influence the chemistry to take the guesswork out of designing new lubricants for advanced materials. The work will also significantly improve our understanding of mechanically induced processes in general. Mechanochemical syntheses have been widely used in organic chemistry to make molecules in a solvent-free environment, to synthesize pharmaceuticals and novel inorganic materials, and mechanical processes are ubiquitous in biology. This work will provide fundamental molecular-scale insights into mechanochemical reactions that will positively impact the United States’ economy. Students gaining experience in the experimental and theoretical methods will provide them with a broad multidisciplinary education in chemistry, physics and materials science and will be specifically targeted at including females and minorities in the research.The project will investigate the gas-phase lubrication of copper by small molecules such as dialkyl disulfides and carboxylic acids. The reaction pathway for the formation of lubricating films will be studied in ultrahigh vacuum to identify the elementary step reactions. Density functional theory calculations carried out under quasistatic conditions have yielded activation energies in good agreement with experimental measurements of mechanochemical reaction kinetics under compression using an atomic force microscope tip. Thus, the research exploits this experimental and theoretical toolbox developed during previous studies to addresses two fundamental issues: 1. To understand and predict the effect of combined normal and lateral stresses on the rates of tribochemical reactions on surfaces and 2. To understand the way in which binding to the substrate and the moving counterface influences tribochemical reactivity. The project will involve outreach to underrepresented undergraduates as well as outreach to Latin America and West Africa.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.