Toward Excellent Tribological Performance as Oil-Based Lubricant Additive: Particular Tribological Behavior of Fluorinated Graphene

Abstract

The poor dispersibility, strong interlayer interaction, and inferior crack resistance ability restrict the employment of graphene as a lubricant additive. Herein, we prepared fluorinated graphene with different F/C ratios by direct fluorination of multilayer graphene utilizing F. Among them, highly fluorinated graphene (HFG) with an F/C ratio of about 1.0 presented prominent thermal stability and excellent tribological performance as an oil-based lubricant additive, whose friction coefficient and wear rate had a 51.4 and 90.9% decrease compared to that of pristine graphene, respectively. It was confirmed that C-F bonds perpendicular to the graphene plane contributed to increasing the interlayer distance and tribological performance of fluorinated graphene, while the randomly oriented CF and CF groups did not count as influential, as demonstrated via X-ray diffraction, X-ray photoelectron spectroscopy, and polarized attenuated total reflection-Fourier transform infrared spectroscopy. Meanwhile, Raman measurements traced the formation process of integrated and stable HFG tribofilm during friction process, and the corresponding stability was attributed to the physical and chemical interactions between HFG and friction pairs. More interestingly, the outstanding crack resistance ability of HFG preserved the sheet structure from destruction due to decreased in-plane stiffness and out-plane stress, thus constructing the tough tribofilm. The simple and feasible preparation makes HFG a promising candidate as advanced lubricant in industrial fabrication.

Dependence of the fluorination intercalation of graphene toward high-quality fluorinated graphene formation

“…There is no doubt that the interlayer distance is a crucial structural factor to regulate the excellent performances of 2D materials. For example, fluorinated graphene has been supposed to become an advanced lubricant, because effective fluorination intercalation decreases the interlayer surface energy and simultaneously increases the interlayer distance, thus improving its self-lubricating ability 13,39. Its self-lubricating ability, determined by the interlayer van der Waals attraction energy ( E vdW ), can be calculated by E vdW = – d 0 4 γ / h 4 , where d 0 = 0.335 nm, γ is the surface energy and h is the interlayer distance 31,40.…”

“…However, here it should be noted that the peeling process needs elaborate operation and that its large-scale application is inevitably restricted. In terms of FHGO, effective fluorination intercalation changes graphene with a disordered lattice due to inevitably possessing multifarious configurations such as boat or chair,13,14 and it also destroys most aromatic regions, thus presenting an amorphous state, as demonstrated by aberration-corrected transmission electron microscopy (AC-TEM) and selected area electron diffraction (SAED) measurements, the results of which can be found in Fig. S14 and S15 †.…”

“…Fluorinated graphene, as an important graphene derivative, effectively regulates the interlayer of graphene, such as increasing the interlayer distance and reducing the interlayer surface energy 12,13. Meanwhile, the introduction of fluorine would result in new properties and functions of the resulting graphene material, which would enable, for example, a tunable energy gap, high functionalization density and fine chemical reactivity, and excellent thermal stability, allowing electromagnetic as well as medical applications 14–17.…”

Effects of ionic liquid on the dispersion and tribological property of graphene lubricant

“…In addition, graphene derivatives and graphenebased composites were also considered as an effective kind of lubricant additive. [7][8][9] However, whatever the form of graphene is, the chemical structure of graphene has very strong van der Waals force between layer and layer, so that it is easily aggregated in the base oil, thereby limiting its application in the domain of lubrication. 10 Therefore, achieving a stable dispersion of graphene lubricant is a challenging task.…”

Graphite fluoride and fluorographene as a new class of solid lubricant additives for high‐performance polyamide 66 composites with excellent mechanical and tribological properties

“…Similar to the relationship between graphite and graphene, the GrF platelets also can be exfoliated to fluorographene (FG) nanosheets with several layers. FG, as the youngest graphene based derivative and the thinnest transparent insulator, exhibits similar properties to GrF but has a smaller size and larger specific surface area compared with GrF, which makes FG an excellent advanced material in many areas, such as solid lubricants, super hydrophobic oleophobic coatings, optoelectronic and thermoelectric devices, electrode materials and so on. The unique properties of FG are caused by the fluoride atoms introduced on the surface of carbon, which changes the hybridization of carbon from sp 2 to sp 3 and increases the interlamellar space in the FG nanosheets .…”