Studies on the Use of Atomically Thin Films for Controlling Friction and Adhesion at Interfaces
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Control of friction and adhesion are widely recognized problems that impact a broad range of materials applications from gears and engine components, to medical implants for joint replacements, to micro- and nano-scaled machine technologies. The drive to design advanced lubrication schemes not only facilitates bringing new technologies online in these areas, but can also play a critical role in terms of improved machine efficiencies, where aggregate energy losses to friction and wear in many sectors of the economy contribute greatly to the daunting challenges of meeting US energy needs. Graphene, a single-atom-thick film of carbon, offers a potential solution to many of the challenges in controlling friction and adhesion at interfaces due to its exceptional electrical and mechanical properties. The majority of the scientific studies on the frictional properties of graphene, however, are on perfectly smooth, idealized surfaces. This award supports fundamental research to understand the properties of atomically thin materials such as graphene in realistic interfaces, which are not perfectly smooth but have fine roughness. These experimental studies will be used to determine what aspects control the properties in atomically thin films of graphene, and how these may be engineered to meet technological needs. Students involved in this project receive multidisciplinary training in materials science, engineering, and surface chemistry and physics, developing proficiency in these areas that are critical for the continued development of US technological competitiveness. The influence of real surface characteristics like surface roughness and adhesive interactions on graphene-based lubricants will be investigated to determine how surfaces and graphene may be engineered to meet technological needs. Importantly, how such materials bind to substrates with controlled nanoscopic roughness will be examined by creating films of fused silica nanoparticles, where surface roughness is determined by particle size. Analogous studies with gold nanoparticulate films will be used to address these same questions for conductive surfaces. Atomic force microscopy and Raman microspectroscopy will be used to understand how these materials conform to substrates with nanoscale roughness, and how this influences its tribochemical reactivity and frictional characteristics. These studies will be paired with molecular dynamics simulations of graphene in asperity contacts under analogous conditions, providing atomically resolved detail of the chemical interactions and mechanical contributions to changes in the chemical, structural, mechanical, and frictional properties of graphene in the asperity-asperity contacts that dominate contact between technologically relevant surfaces.