Tiny, sub-micron sized particles are frequently used as additives in the lubricants to improve their frictional and wear behavior. These particles, due to their size, can enter the contact and protect the surfaces from the direct contact in the cases when the base lubricant is not capable of doing it, as in case of boundary lubrication. If their properties are favorable, the friction and wear may be reduced. On the other hand, tiny particles posses large surface area and tend to form aggregates. It is harder for larger aggregated particles to get into the contact to separate the bodies. Besides, agglomeration reduces the ability of the particles to evenly disperse in the lubricant, which also leads to unstable tribological performance.
Xuan Dou and his colleagues from Northwestern University developed such type of ultrafine particles, which can self-disperse in the lubricant, generating a stable suspension. They used graphene to produce tiny crumpled, paper like balls to use as an additive to polyalphaolefin base oil. These particles have favorable mechanical properties and exhibit chemical and thermal stability. On top of it, the use of these particles shows stable and moreover, superior tribological behavior compared to other widely used carbon based additives. It was also shown by experimental measurements, that the friction and wear coefficients are improved even compared to the commercial fully formulated oil.
It should be noted that the fully formulated oils are highly toxic due to their additives. Development of the graphene based substitute with comparable, or even superior, tribological properties, may also help to reduce the negative impact of the commercial lubricants on the environment.
More details can be found in the original article by Xuan Dou et al, Self-dispersed crumpled graphene balls in oil for friction and wear reduction.
Credit for image: By U.S. Army Materiel Command – https://www.flickr.com/photos/armymaterielcommand/6795812766, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=37863884