Controlling friction of graphene

Graphene-Nanosheet
AFM image of graphene nanosheet [1].

Graphene, a wonder just one atom thick material, shows incredible wear-resistance and super low friction levels. This behavior is ascribed to its low inter-layer shear properties and high normal load carrying capabilities. However, in many cases controlling friction is preferable. Apparently, this is possible with graphene, which makes it even more attractive material in the field of tribology.

Researchers from China recently reported a way to control tribological behavior of graphene sheets using plasma treatment and thermal heat reduction. It was shown that plasma treatment introduces defects (by inducing nitrogen and oxygen containing functional groups) into the surface and their amount increases with treatment time. It was clearly shown, that the defects increase adhesion force (also hydrophilicity) and the time of the plasma treatment determines the degree of growth. According to Bowden and Tabor adhesion friction model, the increase of the adhesion force increases friction and this behavior was confirmed in the current study by the Atomic Force Microscopy measurements of friction on graphene sheets, as shown in the Fig. 1.

Friction vs Plasma Treatment Time
Fig. 1. Friction vs Plasma Treatment Time (PLA-0 corresponds to graphene without treatment, while PLA-12 corresponds to graphene after 12 seconds treatment). Image is taken from [1].
It was observed in the research that the thermal reduction (heating at 750C for 30 min in presence of nitrogen and hydrogen) brings the adhesion force of graphene sheets almost to the level of untreated material. Interestingly, this was not the case with friction force. It was argued that the thermal reduction eliminates the functional groups created during plasma treatment, but it also creates structural defects (vacancy-like) by removing carbon atoms from the graphene lattice as shown in Fig. 2. This brings increased friction.

Defects of graphene
Fig. 2. Generation of functional groups by plasma treatment and their subsequent removal with vacancy-like defects rise after the thermal reduction process [1].
Results of the study can help in design of graphene base coatings in nano tribological applications. Further details can be found in the original article: Zeng, X. et al. Controllable Nanotribological Properties of Graphene Nanosheets. Sci. Rep. 7, 41891; doi: 10.1038/srep41891 (2017).

[1]. Zeng, X. et al. Controllable Nanotribological Properties of Graphene Nanosheets. Sci. Rep. 7, 41891; doi: 10.1038/srep41891 (2017).

Save

Save

Aydar Akchurin
About Aydar Akchurin 35 Articles

Editor-in-Chief, PhD (Tribology), Researcher at ASML, Eindhoven, the Netherlands. Expertise in modeling of lubrication, friction and wear.

2 Comments

  1. I am not sure that Zeng et al. have the control of friction with graphene that they think they have. Remember that graphene has been shown to be self-healing under compression and stress. Induced vacancies (holes) can self-heal over time, reducing the desired induced friction. As the lowest energy state for the carbon matrix is the hexagonal (graphene) configuration, it may be that any induced friction from vacancies is short-lived in a tribological contact setting.

  2. You are right and they also considered the healing of graphene properties with time. They observed a clear trend of decreasing friction on treated graphene to the level corresponding to the untreated graphene, but the full recovery was not achieved (after 8 hours). Self-healing – a nice property of graphene!

Leave a Reply

Your email address will not be published.


*