October 1, 2017.
The superlubricity of graphene, a two-dimensional allotrope of carbon, has been experimentally confirmed in ultralow friction studies. Studies were carried out on a nanoscopic scale, and their results implicated the possibility of using graphene for frictionless coatings. In an attempt to observe reduced friction on the macro scale, we studied 2-3 mm diameter metal spheres coated with monolayer and multilayer graphene via chemical vapor deposition. Graphene-coated and control spheres were dropped through water, isopropanol, and glycerol. The motion of these spheres was recorded using a high-speed camera. Videos were analyzed frame-by-frame to determine the speeds of coated and uncoated metal spheres as they fell. Because graphene’s properties as a superlubricant suggest that coated spheres moving through fluids should experience less drag as they fall, coatings would theoretically influence the rate at which spheres approach terminal velocity. We were not able to observe a difference in the motion between graphene coated and uncoated control samples. This result can possibly be attributed to two factors: (i) non-uniform graphene coating in our test samples and (ii) too small a difference in falling speeds to be measured accurately at the resolution of the equipment used for this experiment. Our results suggest the need for more experimentation or that the friction-reducing qualities of graphene films may not be observable or significant on the macro scale.
San Francisco State University (SFSU)
This material is based upon work supported by the National Science Foundation through the Robert Noyce Teacher Scholarship Program under Grant # 1340110. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The research was also made possible by the California State University STEM Teacher and Researcher Program, in partnership with Chevron (www.chevron.com), the National Marine Sanctuary Foundation (www.marinesanctuary.org) and San Francisco State University.