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. 2020 Jan 19;7(4):1903239.
doi: 10.1002/advs.201903239. eCollection 2020 Feb.

Macroscale Superlubricity Enabled by Graphene-Coated Surfaces

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Free PMC article

Macroscale Superlubricity Enabled by Graphene-Coated Surfaces

Zhenyu Zhang et al. Adv Sci (Weinh). .
Free PMC article

Abstract

Friction and wear remain the primary modes for energy dissipation in moving mechanical components. Superlubricity is highly desirable for energy saving and environmental benefits. Macroscale superlubricity was previously performed under special environments or on curved nanoscale surfaces. Nevertheless, macroscale superlubricity has not yet been demonstrated under ambient conditions on macroscale surfaces, except in humid air produced by purging water vapor into a tribometer chamber. In this study, a tribological system is fabricated using a graphene-coated plate (GCP), graphene-coated microsphere (GCS), and graphene-coated ball (GCB). The friction coefficient of 0.006 is achieved in air under 35 mN at a sliding speed of 0.2 mm s-1 for 1200 s in the developed GCB/GCS/GCP system. To the best of the knowledge, for the first time, macroscale superlubricity on macroscale surfaces under ambient conditions is reported. The mechanism of macroscale superlubricity is due to the combination of exfoliated graphene flakes and the swinging and sliding of the GCS, which is demonstrated by the experimental measurements, ab initio, and molecular dynamics simulations. These findings help to bridge macroscale superlubricity to real world applications, potentially dramatically contributing to energy savings and reducing the emission of carbon dioxide to the environment.

Keywords: ambient conditions; graphene; macroscale superlubricity; macroscale surfaces; molecular dynamics.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic diagrams of fabrication processes for macroscale superlubricity system from a) a ball and plate b) coated with MLG by PECVD, c) then adding GCS dispersed between the GCB and GCP, and d) finally performing macroscale superlubricity under ambient conditions.
Figure 2
Figure 2
Photographs of pristine a) quartz plate, b) SiO2 powder, and c) quartz ball, and after graphene deposition for d) GCP, e) GCS, and f) GCB, g–i) corresponding TEM images, respectively, and j–l) corresponding Raman spectra, respectively. Inset in (e) is the corresponding SEM image. Inset in (j) shows the Raman spectrum of standard high‐quality single layer graphene.
Figure 3
Figure 3
Friction coefficient of a) GCB/GCS/GCP, Ball/MS/Plate, GCB/GCP, Ball/Plate, b) GCB/GCS/GCP, GCB/HOPG, Ball/HOPG as a function of time, and friction coefficient of GCB/GCS/GCP as c) a function of time and d) normal load at different sliding frequencies.
Figure 4
Figure 4
Optical images of the wear track of the GCP after friction tests for a) GCB/GCP (measured at 0.1 Hz), b) GCB/GCS/GCP (measured at 0.1 Hz), and c) GCB/GCS/GCP (measured at 0.5 Hz), d–f) corresponding Raman spectra, respectively, and g–i) corresponding Raman mapping, respectively.
Figure 5
Figure 5
Optical images of the wear areas on the GCB after friction tests under 35 mN for a) GCB/GCP (measured at 0.1 Hz), b) GCB/GCS/GCP (measured at 0.1 Hz), and c) GCB/GCS/GCP (measured at 0.5 Hz), and d) their Raman spectra taken from the corresponding small dots. Wear areas are marked by dotted circles in each figure.
Figure 6
Figure 6
a) Variation of energy per atom as a function of rotation angle, and snapshots of the supercell rotated with the top layer of graphene at rotation angles of b) 8–10°, and c) 30–32°.
Figure 7
Figure 7
a) Friction coefficient as a function of sliding distance, and snapshots of atomic configurations of the top plate wrapped with the graphene sliding at b) 0.3, c) 1.4, d) 1.5, e) 2.1, f) 2.2, g) 2.4, and h) 3.1 nm. Inset in (a) shows the side view of the constructed MD model. Insets marked by the bigger black squares show the corresponding enlarged images marked by the smaller black squares in each figure.
Figure 8
Figure 8
a) Friction coefficient of the GCB/GCP and GCB/GNS/GCP as a function of sliding distance, and typical atomic configurations at different distance of the topmost graphene sheet attached on plate b) without and c) with GNS. a) Dark red, orange, cyan, yellow, light blue and dark blue refer to the scratching tip, MLG on the tip, MLG wrapped on NS, NS, MLG on the plate and plate, respectively. b,c) The colors are coded according to the hydrostatic stress, and atoms with positive and negative values correspond to the tensile and compressive stresses, respectively.

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