Water and other adsorbates present at sliding interfaces affect friction measured across a range of length scales. This effect is particularly significant at the nanoscale, where friction can vary by orders of magnitude depending on the environment. Frictional variation is due to both chemical and physical effects, since adsorbates can physically change the size and morphology of the contact interface as well as chemically interact with the contacting bodies to alter how they slide relative to one another. The presence of adsorbates is particularly evident at surface defects on layered materials, such as step edges on graphite, where friction can increase dramatically relative to the superlubricity observed on a basal plane. Here, we use reactive molecular dynamics simulations to study how water and other adsorbates affect atomic-scale friction on both the basal plane of graphite as well as at the ubiquitous step edges. The simulations capture termination of the step edge and probe as well as chemical reactions and interactions that occur during sliding, which then enables us to isolate the physical and chemical factors that determine friction.<br/>

Friction on graphite in the presence of adsorbates: Physical and chemical effects on the basal plane and at step edge defects

2019 Fall National Meeting

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