2015 05 method friction surfaces macroscopic scale (1)

Researchers demonstrate method thatreduces friction between two surfaces toalmost zero at macroscopic scale15 May 2015, by Bob Yirka

Schematic of the superlubricity test (not-to-scale). Credit:(c) 2015, Science, DOI: 10.1126/science.1262024

(Phys.org)—A team of researchers working atArgonne National Laboratory, in Illinois, has founda way to dramatically reduce friction between twomacroscopic scale surfaces—to near zero. In theirpaper published in the journal Science, the teamdescribes how they accidently discovered themethod and why they believe it might be useful forreal world applications.

As most people are aware, friction causes energyloss and wear and tear on mechanicalparts—lubricants such as oil are used to helpreduce friction and to dissipate heat, but scientistswould really like to find a way to prevent it fromhappening in the first place. In this new effort, theresearchers were studying friction properties at thenanoscale, where it is more about the attractiveforces between atoms, than microscopicimperfections that are present at the macroscopicscale. They were testing an idea they had, that ifone flat material was coated with graphene andanother with a diamond-carbon mixture, there likelywould be little friction when one was slid over the

other.

In looking at their results they noticed thatsometimes they achieved a very low frictioncoefficient, and sometimes they did not. Thedifference, they found, came about when tinydiamonds came off the diamond-carbon surfacewhich were then rolled between the two as thesliding ensued. Suspecting they had something, theteam tried again, but this time after coating thesurfaces, they tossed some nanodiamondsbetween the two, to serve as tiny ball bearings,then slid one surface over the other and found thefriction between them was so low that it qualified assuperlubricity.

In taking a closer look at what actually occurredduring the sliding, the researchers found that as thenanodiamonds rolled under the graphene, theybecame coated with flakes (creating what the teamcalls scrolls) and that was why the friction betweenthe two surfaces remained consistently low for theduration of the sliding. They tested the methodunder varying conditions, such as changing thesliding speed, the load and the temperature, andfound that it worked under a most such condition,with the exception being, high humidity—watergummed up the works. The team believes themethod could be used in electronic components, orperhaps in space based applications whereenvironments are carefully controlled.

More information: Macroscale superlubricityenabled by graphene nanoscroll formation, Science, DOI: 10.1126/science.1262024

ABSTRACTFriction and wear remain as the primary modes ofmechanical energy dissipation in movingmechanical assemblies, thus it is desirable tominimize friction in a number of applications. We

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demonstrate that superlubricity can be realized atengineering scale when graphene is utilized incombination with nanodiamond particles anddiamond-like carbon (DLC). Macroscopicsuperlubricity originates because graphene patchesat a sliding interface wrap around nanodiamonds toform nanoscrolls with reduced contact area thatslide against the DLC surface, achieving anincommensurate contact and significantly reducedcoefficient of friction (~0.004). Atomistic simulationselucidate the overall mechanism and mesoscopiclink bridging the nanoscale mechanics andmacroscopic experimental observations.

© 2015 Phys.orgAPA citation: Researchers demonstrate method that reduces friction between two surfaces to almostzero at macroscopic scale (2015, May 15) retrieved 9 July 2015 from http://phys.org/news/2015-05-method-friction-surfaces-macroscopic-scale.html

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