Diamond-like carbon (DLC) films directly deposited on rubber substrate is undoubtedly one optimal option to improve the tribological properties due to its ultralow friction, high-hardness as well as good chemical compatibility with rubber. Investigating the relationship between film structure and tribological performance is vital for protecting rubber. In this study it was demonstrated that the etching effect induced by hydrogen incorporation played positive roles in reducing surface roughness of DLC films. In addition, the water contact angle (CA) of DLC-coated nitrile butadiene rubber (NBR) was sensitive to the surface energy and sp² carbon clustering of DLC films. Most importantly, the optimum tribological performance was obtained at the 29 at% H-containing DLC film coated on NBR, which mainly depended on the following key factors: (1) the DLC film with appropriate roughness matched the counterpart surface; (2) the contact area and surface energy controlled interface adhesive force; (3) the microstructure of DLC films impacted load-bearing capacity; and (4) the generation of graphitic phase acted as a solid lubricant. This understanding may draw inspiration for the fabrication of DLC films on rubber to achieve low friction coefficient.

Diamond-like carbon (DLC) films are deposited on rubber surfaces to protect the rubber components, and surface pretreatment of the rubber substrates prior to the film deposition can improve the adhesion between the DLC films and the rubber. Thus, the principal purpose of this work concentrates on determining the effects of argon (Ar), oxygen (O₂), nitrogen (N₂), and hydrogen (H₂) plasma pretreatments on the adhesion and friction performance of the DLC films deposited on rubber (DLC/rubber). The results indicated that the Ar plasma pretreatment promoted the formation of a compact layer on the rubber surface. By contrast, massive fillers were exposed on the rubber surface after oxygen or nitrogen plasma pretreatments. Moreover, the typical micrometer-scale patches divided by random cracks were observed on the surface of DLC/rubber, except for the sample pretreated with oxygen plasma. The adhesion of DLC/rubber was found to strengthen with the removal of weak boundary layers and the generation of free radicals on the rubber surface after plasma pretreatment. The tribo-tests revealed that DLC/rubber with O₂, N₂, and H₂ plasma pretreatments cannot achieve optimal friction performance. Significantly, DLC/rubber with Ar plasma pretreatment exhibited a low and stable friction coefficient of 0.19 and superior wear resistance, which was correlated to the high adhesion, good load-bearing of the rubber surface, and the approximate sine function of the surface profile of the DLC film.

Fluorine-incorporated hydrogenated fullerene-like nanostructure amorphous carbon films (F-FLC) were synthesized by employing the direct current plasma enhanced chemical vapor deposition (dc-PECVD) technique using a mixture of methane (CH₄), tetra-fluoromethane (CF₄), and hydrogen (H₂) as the working gases. The effect of the fluorine content on the bonding structure, surface roughness, hydrophobic, mechanical, and tribological properties of the films was systematically investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman analysis, atomic force microscope (AFM), contact angle goniometer, nano-indenter, and reciprocating ball-on-disc tester, respectively. The fluorine content in the films increased from 0 to 2.1 at.% as the CF₄ gas flow ratio increased from 0 to 3 sccm, and incorporated fluorine atoms existed in the form of C–F_X (X = 1, 2, 3) bonds in the film. The fullerene nanostructure embedded in the hydrogenated amorphous carbon films was confirmed by Raman analysis. The water contact angle was significantly increased because of fluorine doping, which indicates that the hydrophobicity of the carbon films could be adjusted to some extent by the fluorine doping. The hardness and elastic modulus of the films remained relatively high (22 GPa) as the fluorine content increased. Furthermore, the friction coefficient of the carbon films was significantly reduced and the wear resistance was enhanced by fluorine doping.