Sandia National Labs Academic Programs Collaboration Report

Fundamental mechanisms of friction evolution in lamellar solids

A variety of precision electromechanical devices in commercial aerospace and Sandia mission applications require critical solid lubricants because frictional performance changes during operation and storage in reactive atmospheres, thus restricting usage and limiting device designs. The LDRD project, led by PI Michael Dugger, focused on understanding the atomic scale processes responsible for the evolution of friction coefficient in 2D lamellar materials. Recent research on molecular electronics motivated the first use of ‘work function’ to provide insights on atomic structure and defect content of worn surfaces and, with molecular dynamics simulations, showed that water increases the friction coefficient exhibited by MoS 2 (an exemplar lubricant) through disrupting the shear-induced restructuring of the surface into large, ordered lamellae. Sandia partnered with Florida A&M and Florida State University’s joint College of Engineering, which developed a novel way to look at transfer films resulting from contact of lamellar solids. The

resulting understanding will inform the design of tailored nanocomposites that suppress aging mechanisms and significantly improve reliability and performance of solid lubricants.

Work function (bottom) of MoS 2 wear tracks showing structure modification of surface lamellae (top left) due to environment. Atomistic simulations of MoS 2 (upper right) show water clustering at S vacancies.

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Academic Programs