A Direct Experimental Link Between Atomic-Scale and Macroscale Friction

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Friction governs the operating limitations, durability, energy consumption, and control of virtually every machine including those with important implications for healthcare, economic prosperity, and national security. Although we sense friction at the macroscale, it is known to originate at the atomic-scale. Despite having scientific roots dating back to da Vinci, our understanding of how these fundamental atomic-scale interactions contribute to everyday friction remains poor. This award will support a controlled study of interfacial friction from the atomic-scale to the practical-scale to elucidate this relationship. The results will be used to develop a testable model of frictional scaling. Such a model is needed to inform materials design and surface engineering efforts for friction control applications. The results will translate to practice through our existing collaborations with industrial partners whose products all make extensive use of the model solid lubricant material studied here. Lastly, the project funds an educational effort that reaches 6-12th grade populations, university students and faculty, and the broader scientific community. Atomic force microscopy enables fundamental studies of atomic-scale friction phenomena whereas traditional tribometry measures friction at the more practical macro-scale. A lack of the tools needed to study the length, force, and speed scales in between has prevented the community from linking machine friction to its fundamental origins. The team on this project has developed two key technologies to enable this project: 1) a method to reliably calibrate and quantitatively measure atomic-scale friction and 2) a microtribometer capable of bridging measurements from the atomic-scale to those from the macroscale. The objective of this project is to stitch these length-scales together by carefully controlling material, load, probe radius and speed in the gap between the atomic and macro size-scales. The results will be used to develop a testable scaling model for interfacial friction that will enable our materials scientist collaborators to design materials and engineer interfaces for improved frictional control. To promote translation of the science to broader audiences, the team will: 1) publish in the most visible journals; 2) present at high impact conferences; 3) educate collaborators; 4) inject practices and outcomes into instruction; 5) mentor graduate and undergraduate students in research; and 6) engage 7-12th grade populations by conducting outreach activities on campus and at tribology conferences.