Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface

Carbon-based layers play an important role in boundary lubrication, from graphite as commercial solid lubricant in a spray can over diamond-like carbon coatings in automotive industries all the way to graphitic layers found in metal-metal hip implants. With increasing availability of graphene, the two-dimensional building block of graphite, its possible role in lubrication is being explored. *

After the discovery of friction and wear reduction on steel surfaces by graphene in a variety of environments, graphene is now emerging as new lubricant. Polymer composites with graphene exhibit improved tribological properties due to wear reduction by efficient transfer layers. The composite approach has been successfully extended to multilayers of polymer and graphene. The use of graphene as additive in formulated lubricant oils is also promising after functionalization to improve solubility. *

In their letter “Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface” G. Krämer, C. Kim, K-S. Kim and R. Bennewitz report experimental results for fundamental lubrication properties of the interface between a hexadecane model lubricant and a steel surface modified by a single layer graphene. Using high-resolution force microscopy, they quantify that the reduction of friction on graphene is connected to an ordered layer of adsorbed hexadecane molecules and that the graphene induces an ordering in molecular layers in the confined liquid above graphene patches. *

A single layer of graphene on steel surfaces causes a change in the near-surface structure of the model lubricant hexadecane. Hexadecane adsorbs in an ordered layer aligned straight molecules, and this layer is stable under scanning in contact with the tip of an atomic force microscope, while no such layer is observed on the steel substrate. Graphene and hexadecane layer reduce friction at the nanoscale by a factor of three compared to the bare steel in hexadecane. *

All AFM measurements described in this letter were performed using a NANOSENSORS™ PointProbe® Plus PPP-CONTR AFM probe at room temperature with a home-built fluid cell where the cantilever was fully immersed in hexadecane.*

 Figure 3 from “Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface” by G Krämer et al.:
 High-resolution lateral force maps recorded in hexadecane with a normal force of 3 nN. (a) On graphene, the adsorbed hexadecane molecules arrange in form of lamellae with a width of 2.1 nm. The cross-section was taken along the line indicated. The schematic depiction of the orientation of one hexadecane molecule is informed by the results in [21]. (b) On the steel substrate, an irregular stick-slip pattern with a characteristic slip length of about 1 nm is observed. The two cross-sections are taken the along the lines indicated in the respective color.
Figure 3 from “Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface” by G Krämer et al.:
High-resolution lateral force maps recorded in hexadecane with a normal force of 3 nN. (a) On graphene, the adsorbed hexadecane molecules arrange in form of lamellae with a width of 2.1 nm. The cross-section was taken along the line indicated. The schematic depiction of the orientation of one hexadecane molecule is informed by the results in [21]. (b) On the steel substrate, an irregular stick-slip pattern with a characteristic slip length of about 1 nm is observed. The two cross-sections are taken the along the lines indicated in the respective color.

*G. Krämer, C. Kim, K-S. Kim and R. Bennewitz
Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface
Nanotechnology, Volume 30, Number 46, 2019, 46LT01
DOI: https://doi.org/10.1088/1361-6528/ab3cab

Please follow this external link to read the full article: https://iopscience.iop.org/article/10.1088/1361-6528/ab3cab

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