Synergetic lubrication of Cross-Linked Nanocomposites and Enhanced the tribological performance of Ti-DLC film

Synergetic lubrication of Cross-Linked Nanocomposites and Enhanced the tribological performance of Ti-DLC film | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Synergetic lubrication of Cross-Linked Nanocomposites and Enhanced the tribological performance of Ti-DLC film Hongjiang Mou, Wenqiu Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3996457/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Two-dimensional(2D) nanocomposites exhibit theoretically and experimentally considerable promise for lowering friction and dissipating energy in dry sliding. However, a significant obstacle still stands in lower friction by introducing the 2D nanocomposites in oil lubrication environment. Here, g-C3N4/GO nanocomposites with a 2D layered structure were synthesized successfully. Ti-DLC film was used to examine the tribological performance of graphene oxide (GO), graphitic carbon nitride (g-C3N4), and carbon nitride/graphene oxide (GO/g-C3N4) nanocomposites in oil. As lubrication additives, the friction-reducing and anti-wear properties of GO/g-C3N4 nanocomposites were superior than a single nanomaterial of GO or g-C3N4 nanosheets. The synergistic lubricating effect involves the easy interlayer shear resulting from the oleophilic and distinct microscopic heterojunction stacking structure of the GO/g-C3N4 nanocomposites. This led to the formation of an adsorption lubrication film containing PAO6, g-C3N4, and GO. These innovative investigations have demonstrated that adding 2D GO/g-C3N4 nanocomposites into PAO6 is an intriguing approach to improving the dependability and energy efficiency of current mechanical systems. graphene oxide graphitic carbon-nitrogen Ti-DLC oil lubricant additives tribological performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Friction and wear lead to nonrenewable energy resource exhaustion and mechanical system invalidation[1]. Friction and wear are major factors in a variety of applications, including microscale devices, bio-related devices like teeth and implants, and traditional bearings, pistons, and gears[2-5]. Reducing oil consumption and related environmental pollution requires more efficient friction control ways. Employing a lubricant is the most efficient way to control or reduce wear and friction[6], which was invented as early as 2400 BCE to move the heavy stones utilized for pyramid construction, as described in ancient frescos in Egyptians[7]. The most commonly used method is to add additives, which can form a mechanical film between friction components including reducing friction, anti-wear and corrosion. However, the old single lubrication additives with limitations contain environmental pollutants, and can’t adapt to a variety of working conditions. Therefore, the preparation of environmentally friendly composite lubricant additive with the simultaneous functions of friction reduction, anti-wear, and repair is urgent to adapt to the current technological progress.2D nanomaterials have intensively shown excellent performance in tribology and lubrication due to layered structures[8]. High modulus and strength between monolayer, as well as low interlayer shear strength between neighboring layers, make them ideal for lubricating dual rubbing surfaces[9, 10]. In addition, 2D nanomaterials have a significantly higher specific surface area, allowing them to cover a larger surface area when absorbed on the substrate surface, limiting direct contact with friction surfaces[11]. Graphitic carbon nitrogen (g-C 3 N 4 )[12, 13] has garnered plenty attention recently. The layered structure of g-C 3 N 4 consists of tri-striazine units (as the basic building block), which are joined with tertiary amino groups. Weak van der Waals forces allow the sheets of g-C 3 N 4 to interact with one another to form bulk g-C 3 N 4 materials[14]. It has great thermal and chemical stability[15] and high mechanical properties (elastic modulus 320 GPa and hardness 25 GPa)[16], all of which make it a promising candidate for a revolution green lubricant additive. In addition, this kind of nanomaterial does not contain metal elements, has good biocompatibility and low toxicity, and has good application prospects in the field of biological detection[17]. However, the tribological performances of single g-C 3 N 4 nanomaterial are not enough. Modification technology based on g-C 3 N 4 nanomaterial is time-consuming and cumbersome, and the efficiency needs to be further improved. Therefore, modification of g-C 3 N 4 nanomaterials construct materials with excellent lubrication properties according to practical application requirements. It will be the key to the promotion and application of this material in the field of friction lubrication. Graphene, an emerging 2D nanomaterial, has gained popularity for its exceptional properties, such as high electron mobility, high Young's modulus (~1 TPa), remarkable thermal conductivity, excellent electrical conductivity, and optical transparency. The microscopic and macroscopic tribological behaviors of graphene have been investigated by the academic community since discovered in 2004, it has shown an alluring prospect as a green lubrication additive[18]. The flakes move quickly until they reach a new commensurate location on the microscale, which is caused by a tip-induced change from a commensurate to an incommensurate registry with the underlying graphene layer (the superlubric state)[19]. On the macro-scale, ultrafine particles resembling miniaturized crumpled paper balls as a high-performance additive could self-disperse in oil and act like nanoscale ball bearings to reduce friction and wear and significantly improve the lubrication properties of polyalphaolefin base oil[20]. Nanocomposites composed of two nanomaterials could typically generate effects that are not possible with a single nanomaterial. Taking the combination of 0D and 2D nanomaterials, the pathway of nano diamond and graphene was proposed to improve the tribological properties of hydrogenated amorphous carbon (a-C: H) in ambient air[21]. In-situ growth of nanostructured tribo-layers determines the bonding characteristic of a-C: H film and the tribo-induced structural evolution of lubricants. Interlayer friction of heterostructures achieves superlubricity properties by means of interlayer couplings[22]. The hydrophilization of the BP-GO hybrid nanomaterials makes it easier for water molecules to adsorb on surfaces and penetrate between layers[23]. The unique heterojunction stacking structure further reduced the shear strength, endowed the fascinating prospect of the lubricating properties of DLC. Graphene and MoS 2 composites could provide low friction and wear between DLC and steel[24]. At the frictional interface, MoS 2 was dissolved into Mo and S at high contact pressure. It is contributed to convert the DLC into amorphous carbon and graphene, which provides a low shear sliding and results in low friction and wear. Experimental and theoretical simulations have confirmed that the lateral interactions between two incommensurate contacting surfaces of graphene and hexagonal boron nitride (h-BN) could be effectively counteracted to achieve a robust heterojunction, resulting in ultralow sliding friction[25-27]. The above discussions in the experiments and theory have verified that 2D nanocomposites, by forming van der Waals heterojunctions and disproportional contact, can efficiently minimize friction and energy dissipation. However, achieving low wear and low friction by using 2D nanocomposites in oil remains a major challenge to overcome. Therefore, further exploration of the way to make DLC less friction and wear in oil-based lubrication environments is still needed. In this work, GO/g-C 3 N 4 nanocomposites were successfully synthesized by the self-assembly method, and the oil dispersion stability of two-dimensional nanomaterials was modified by octadecyl amine. The tribological performance of 2D nanocomposite as a lubricant was evaluated by contacting GrC15/ Ti-DLC friction pair. In the subsequent step, the lubrication mechanism of the nanocomposite and Ti-DLC film was discussed based on the experimental results. 2 Experiment details 2.1 Materials The graphene oxide powder (GO, 99%), N-methyl pyrrolidone (NMP, ≥99.5%) and octadecylamine were suppliers by Shanghai Aladdin Biochemical Technology Co., Ltd. The The pyrolysis of urea in a muffle furnace produced the g-C 3 N 4 nanosheets using the following procedure: First, heat 100 g of urea in an alumina crucible for 40 minutes at a rate of 4 °C/min. Next, increase the temperature to 560 °C at rate of 2 °C/min and holding for 100 min. the obtained buck g-C 3 N 4 was collected into weighing bottle, after a natural cooling process. Anhydrous ethanol (99.7%) originated from Tianjin Bohua Pharmaceutical Chemical Co., Ltd., China. 2.2 Synthesis of GO/g-C 3 N 4 O Nanocomposites NMP is an excellent organic solvent[28] to exfoliate 2D material, and it has been demonstrated that a saturated NMP solution could increase the stability of the prepared 2D nanosheets[29]. The presence of NMP solution has no effect on the structure or morphology, 200 mL of NMP solution was mixed with 60 mg of g-C 3 N 4 and GO powder, and ultrasonic exfoliation was then performed for 4 hours in ice water bath kepting below 30 °C. The mixture nanosheets dispersion was centrifuged at 9000 rmp min - 1 for 10 min after ultrasonic exfoliation, to generate a mixture nanosheets dispersion. The GO/g-C 3 N 4 nanocomposite was obtained via washing the leftover NMP in absolute ethanol. Since there were no chemical interactions during this self-assembling process, the main driven force that combined g-C 3 N 4 with GO was the van der Waals force. It is well known that inorganic nanoparticles are poor dispersion stability in organic liquids, thus requiring the same concentration of surfactant to improve dispersion. Octadecylamine was utilized as a dispersing agent. In the subsequent step, the ethanol dispersion of the octadecylamine (2mg/mL -1 ) was added drop-wise into the anhydrous ethanol dispersion of the GO/g-C 3 N 4 nanocomposites while stirring continuously at 800 rpm and the temperature of 70°. The reaction mixture was then refluxed for 24 hours. The octadecylamine-modified GO/g-C 3 N 4 nanocomposites were thoroughly washed with ethanol and then separated by vacuum filtration using a membrane filter. The washing and filtration were repeated four times to obtain the modified GO/g-C 3 N 4 nanocomposite. The single g-C 3 N 4 and GO were modified with same way. 2.3 Dispersion stability test of Modified Nanocomposites In order to investigate the dispersion stability of composite nanomaterials in PAO6, the g-C 3 N 4 , GO and GO/g-C 3 N 4 were ultrasonically dispersed into PAO6 for 30min, respectively. To prepare dispersion of g-C 3 N 4 /GO nanocomposite, firstly the g-C 3 N 4 and GO oil dispersions were prepared by mechanical depolymerisation process, respectively. In the process, 0.01 wt%, 0.02 wt%, 0.04 wt%, 0.06 wt%, 0.08 wt% and 0.1 wt% of g-C 3 N 4 and GO powders were dispersed in PAO6, respectively. Subsequently, the 0.04 wt% g-C 3 N 4 /GO nanocomposite dispersion was ultrasound for 20 min, utilizing an ultrasonic probe (Branson Digital Sonifer 450, USA) at a power of 400 watts for 10 min with a 10s on/off interval. Figure 1 depicts dispersion results after sonication and 7 days of undisturbed ambient air. The dispersion test reveal that nanosheets modified with octadecamine effectively disperse in PAO6 oil, PAO6 base oil was also employed as a baseline for comparison. The long-term dispersion stability of modified nanosheets was attributed to their high specific surface area along with presence of ample alkyl chains. The van der Waals interaction between the octadecyl chains of modified nanosheets and alkyl chains of PAO6 oil causes nanosheets to distribute completely and ensure long term stability. The high specific surface area and abundance of alkyl chains were responsible for the long-term dispersion stability of modified nanosheets. 2.4 Characterization The size distributions of the GO, g-C 3 N 4 and GO/g-C 3 N 4 nanocomposites, were measured by a particle analyzer (Litesizer 500). Transmission electron microscopy (TEM, TecnaiG2 TF20) combined energy dispersive X-ray (EDX) microanalysis and field emission scanning electron microscopy (FESEM, JSM 6701F) were carried out to determine morphology and elements of product. A TEM microgate with a carbon support film was utilized as a carrier for the prepared nanomaterial. Scanning electron microscopy (SEM, TESCAN, MIRA3) equipped with energy dispersive spectroscopy (EDS, XFlash 6130, Bruker) was used to observed the morphology of wear tracks and wear scars and distribution of elements. A X-ray photoelectron spectra (XPS, ESCALAB 250Xi.) was employed to record the chemical compositions and chemical bonding in the wear scar. The X-ray diffraction patterns (XRD) were recorded by an EMPYREAN. 2.5 Tribological tests of GO/g-C 3 N 4 nanocomposites Tribological tests ofTi-DLC film subjected to lubricated sliding against GrC15 ball with a diameter of 10 mmwere carried out on a UMT-TriboLab (Bruker. US) in ball-on-disc reciprocating mode sliding for 1.44 km. All the tests were conducted at ambient temperature with amplitude of 2 mm, sliding frequency of 10 Hz, a sliding time of 1h and a normal load of 200 N which corresponded to a maximum Hertzian contact pressure of approximately ∼1.6 GPa. A microsyringe was used to drop 50 μl of lubricant into the contact region after the lubricant had been ultrasonically mixed for 0.5 hours to create a stable and uniform suspension. All the disks and dual balls had been ultrasonically degreased with ethanol to remove contaminants before each test. Following friction tests, the worn surfaces and dual balls were cleansed by acetone. A non-contact three-dimensional (3D) surface profiler (MicroXAM-800, KLA-Tencor, USA) was employed to calculate the wear loss of each wear track at five randomly locations. 3 Results and discussion 3.1 Chemical and Structural of the GO/g-C 3 N 4 nanocomposites The size distribution of GO, g-C 3 N 4 and GO/g-C 3 N 4 nanocomposites was examine by a particle analyzer in Figure 2 . The results showed that GO nanosheets ranged from about 590 to 1120 nm ( Figure 2a ), while g-C 3 N 4 nanosheets was concentrated around 290-650 nm ( Figure 2b ). Particle sizes in the GO/g-C 3 N 4 nanocomposites range from 200 to 1216 nm ( Figure 2c ), indicating that the friction process has no effect on one another’s structure or size. Figure 3 presents the fine microstructure and SAED patterns of GO, g-C 3 N 4 and GO/g-C 3 N 4 nanocomposites. Figure 3a illustrates how GO nanosheets with a handful of layers are usually crinkled and entangled in in a few square micrometers areas. Selected area electron diffraction (SAED) images demonstrate clearly defined diffraction rings, indicating that the GO nanosheets have a crystalline and well-ordered structure. The g-C 3 N 4 noosheets display an individual layer or stack of many layers, like a typical agglomeration in Figure 3b . More importantly, the g-C 3 N 4 nanosheets have a smaller size than GO nanosheets. Figure 3c shows that the GO/g-C 3 N 4 nanocomposite has numerous g-C 3 N 4 nanosheets decorated on the surface of GO. The particles size of g-C 3 N 4 nanosheets is about 543 nm, while the particles size of GO nanosheets is approximately 959 nm, which is consistent with the size distribution in Figure 2 . Meanwhile, EDX analysis is further confirmed that the formation of GO/g-C 3 N 4 nanocomposite appear strong intensity peaks corresponding to N element ( Figure 3d ). A small amount of O elements may be caused by graphene oxidation. These findings collectively verify that GO and g-C 3 N 4 nanosheets coexist in the GO/g-C 3 N 4 heterostructure. Furthermore, FESEM revealed the microstructure of the GO, g-C 3 N 4 and GO/g-C 3 N 4 nanocomposites. Figure. 4a reveals that GO has a few-layered and wrinkled structure. The size distribution of g-C 3 N 4 nanosheets is small than GO (about 400 nm) in Figure. 4b . Several minute particles of g-C 3 N 4 load on the surfaces of GO, resulting in a layer-by-layer hybrid structure of GO/g-C 3 N 4 in Figure 4c . XRD diffraction peaks of the GO, g-C 3 N 4 and g-C 3 N 4 / GO nanocomposites were investigated to explore the structural alterations in Figure 5 . The (100) peak of g-C 3 N 4 at 13.1° corresponds to the in-plane structural packing of nitrogen-linked heptazine units with a lattice distance of 0.676 nm. The (002) peak at 27.5° indicates aromatic graphite lattices with an interplanar stacking distance of 0.324 nm[30, 31].The characteristic peak of GO, C (002), appears at 21°, indicating a smaller interlayer spacing of 0.41nm, approximately. This is significantly larger than characteristic interlayer spacing of graphene (0.34 nm)[32, 33]. This indicates that the oxygen function has vanished on the basal planes of the alkylated GO nanosheets. At this stage, weak van der Waals contacts can join the lamellas of alkylated GO nanosheets since the sp2 carbon skeleton fails to contain any oxygen functionalities[33]. In GO/g-C 3 N 4 nanocomposites, the unbroken GO structure is represented by the peak at 21°, while the g-C 3 N 4 structure is indicated by the peak at 27°, indicating that the g-C 3 N 4 decorating on the surface of the GO nanosheets are not affect each other. The peak of g-C 3 N 4 at 13.1°vanished because decreases of in-plane structure accumulation. This might result from the GO nanosheet combination; intercalation structure could emerge. 3.2 Tribological Properties of the GO/g-C 3 N 4 nanocomposites as Lubricant Additives The lubrication properties of GO and g-C 3 N 4 were investigated independently. Figure 6a and 6b displays the average coefficient of friction (COF)and wear rate of wear scar when lubricated with varying concentrations of GO-dispersion and g-C 3 N 4 - dispersion, separately. PAO6 is 0 wt% as comparison. Figure 6a shows that as concentrations increased, the COF and wear rate first decreased and then reached a minimum at 0.04 wt%. From there, as concentrations increased further, the COF increased while the wear rate remained essentially unchanged. At the optimal concentrations, the wear rate decreased by approximately 85.8% and the COF decreased by around 20%, from 0.1 to 0.08, in comparison to PAO6. The average COF and matching wear rates of the g-C 3 N 4 -dispersions at various concentrations are displayed in Figure 6b . Similar variations trend emerged, the lowest COF and wear rate appear at 0.04 wt% and 0.06 wt%, and lowered by 10% and 83% comparing to PAO6, respectively. The optimal concentration of g-C 3 N 4 is considered to be in the range 0.04-0.06 wt%. It is impossible to ignore that the optimal concentration of g-C 3 N 4 -dispersion is considerably higher than GO-dispersions, which is most likely because of smaller particles size and better dispersion of g-C 3 N 4 . In summary, g-C 3 N 4 -dispersions and GO-dispersions may provide excellent lubrication performance at concentrations ranging from 0.04 to 0.06wt%. When the concentration was relatively low, effective lubricating films could not be formed because insufficient nanosheets could enter the contact area, so COF and wear rate decreased with the increase of concentration. Nevertheless, overabundance of nanosheets might lead to unstable dispersion and rather massive agglomerates, which will exacerbate wear. Based on the above experimental results, 0.04 wt% concentration was chosen as the optimal concentration to investigate the lubricant mechanisms of GO/g-C 3 N 4 nanocomposites. Friction coefficients and wear rates of three lubricants were shown in Figure 7 . Obviously, the GO/g-C 3 N 4 -dispersions exhibits the most wonderful potential; its friction coefficient and wear rate were approximately reduced by 18% and 89.9%, respectively, compared with control of pure PAO6. The lubricant properties of GO/g-C 3 N 4 nanocomposite are superior to those of GO or g-C 3 N 4 alone. Outstanding anti-friction and anti-wear effect of GO/ g-C 3 N 4 may originate from the synergistic lubrication action of the two units. 3.3 Wear surface analysis Figure 8 exhibits the SEM images of wear scars and wear tracks of Ti-DLC under the load of 200N, and the boundary of the wear scar and wear track was marked with white line. Under PAO6 lubrication conditions ( Figure 8a and 8b ), the wear scar area is broad and the wear tracks has furrows and scratches that displayed with an evidence of complete film failure. Under g-C 3 N 4 dispersion lubrication condition ( Figure 8c and 8d ), Certain scattered bright spots appeared on the wear surface, indicating damage in some areas of film, nonetheless the area of wear scar is smaller than that of PAO6. While GO ( Figure 8e and 8f ) and GO/g-C 3 N 4 ( Figure 8g and 8h ) dispersion lubrication conditions, the wear tracks displayed entire film, smallest wear scar diameter, and the shallowest pear ditch. Only a faint rim of the contact area can be observable. The ball and film inside white rim appear clean and similar to the outside region. Therefore, GO/g-C 3 N 4 nanocomposites combining the anti-wear property of GO and the anti-friction peculiarity of g-C 3 N 4 , fully demonstrate their advantages in oil lubrication environments. Figure 9 illustrates the elemental distribution in the wear scars on the steel ball. The wear scar generated with the POA6 exhibited the lowest C content, a small quantity of Ti content, and a strong peak of Fe in Figure 9(a), where Fe originating from the steel ball, C regarding the steel ball and Ti-DLC film, and Ti over the Ti-DLC film. The outcome suggests that the transferred material was mainly from the Ti-DLC film. The wear scar lubricated with GO dispersion appeared a strong peak for C in Figure 9(b) , indicating that the GO layers adsorbed on the contact interfaces. Besides C, Fe and Ti elements, it determines a mass of N elements (3.17 at%) in the wear scar Figure 9(c) . These elements are obviously from the g-C 3 N 4 additives, indicating that the g-C 3 N 4 nanosheets transferred to surrounding area. Additionally, peaks of Fe, Ti and O as well as relatively high concentrations of C and N appeared in Figure 9(d) when the wear scar lubricated with the GO/g-C 3 N 4 -dispersions. Which indicated that g-C 3 N 4 and GO nanosheets might be in charge of the enhanced tribological performance by transferring to the contact area and forming a lubricating film around synergy with the Ti-DLC film. To investigate the particle size changes of additives after the lubrication experiments, the particle sizes distribution of GO and g-C 3 N 4 nanosheets were measured utilizing same particle analyzer in Figure 10 . The particle sizes of GO and g-C 3 N 4 become smaller than those before friction test in Figure 2 . This indicates that the flake additives were triturated during the friction process. Nevertheless, the morphology of the GO/g-C 3 N 4 nanocomposite was preserved from grinding to an extent when GO and g-C 3 N 4 were employed in combination. Curve-fitted XPS spectra of C1s, O1s, Fe2p, and N1s on the wear scar lubricated with 0.04 wt% GO/g-C 3 N 4 -dispersions illustrated in Figure 11 . Figure 11 a illustrates that the C-C peak at 284.5 eV reflects amorphous carbon, which form by GO and the deposition of Ti-DLC film. The peaks at 286.5 eV and 288.2 eV are assigned to the C-N, N-C-N backbone in the g-C 3 N 4 respectively[34]. In Figure 11b, the O1s peak at 532.1 eV was indexed to hydroxides, indicated that adsorbed film derived from the GO or/and organics containing hydroxides. In Figure 11c , the Fe 2p of the Fe 2 O 3 groups was represented by the Fe 2 p 3/2 and Fe 2 p 1/2 peaks ,which were located at binding energies of 711.1 and 724.7 eV[35], respectively. These results verify that the total prevention of the tribo-oxidation is not possible. In Figure 11d , N 1s spectrum with two fitting peaks at 398.7 eV and 400.5 eV were ascribed to N-C=N group of g-C 3 N 4 and the nitrogen in tertiary N -C3 group of g-C 3 N 4 [36]. Therefore, it is reasonable to assume that the GO/g-C 3 N 4 of the nanocomposites was deposited on the contact surfaces, where it formed a physical protective film which served as a barrier during the rubbing process. 3.4 Discussion on lubrication mechanism Based on the above analysis, in Figure 12 vividly summarized the speculated mechanism for the excellent performance of GO/g-C 3 N 4 nanocomposites as additives sliding against Ti-DLC film. The GO/g-C 3 N 4 nanocomposites was modified with octadecylamine during the synthesis process, which results in adsorbed alkyl chain on the surfaces of the 2D nanosheets. The synthesized GO/g-C 3 N 4 nanocomposites uniformly and stably dispersed in PAO6 oil, guaranteeing the continuous supply of additives to the contact surface during the sliding process. The dangling bonds on the surface of the Ti-DLC film may be passivated by the organic chain adsorbed on the GO and g-C 3 N 4 surfaces, which would encourage the decrease of friction. Additionally, the modified GO/ g-C 3 N 4 has the ability to absorb oil molecules from the surface and penetrate between layers, which helps to decrease the interlayer shear stress, thicken the oil film, and keep friction pairs from coming into direct contact. As g-C 3 N 4 and GO are typical 2D layered materials with very low inter-laminar shear strengths, GO/g-C 3 N 4 nanocomposites form a 2D van der Waals heterojunction microscopically through self-assembly. The shear strength is further reduced because the lattice mismatch. The g-C 3 N 4 nanosheets are easily to deposit on micro-pits and repair the contact surface because of their extremely small size (Figure 2). Figure 11 indicated that a few GO nanosheets may be distorted and ruptured because of friction force and heat after a period of sliding time. And then g-C 3 N 4 nanosheets are exposed and released. In addition, to bear the load and separate the friction surface, the released g-C 3 N 4 nanosheets can prevent GO from grinding and repair the ruptured film, thereby extending the durability of the deposition film. Since the high contact pressure creates stressed zones of traction and compression, they produced a thin physical lubricating film on the Ti-DLC film. It’s special layered stacking structure helps the two contact surfaces slide, resulting in low friction behavior. The lubricating film that forms will keep the two contact surfaces from coming into direct contact during the sliding process. Last but not the least, the excellent thermal resistance of the composites can reduce the friction heat and shield them from the damaging effects of high temperature, which results in the remarkable tribological properties[37]. 4 Conclusion In this work, the GO/g-C 3 N 4 nanocomposites are successfully synthesized utilizing self-assembly. Alkylated graphene, g-C 3 N 4 and GO/g-C 3 N 4 nanocomposites nanosheets could thoroughly disperse in the PAO6 oil. The van der waals interaction between octadecyl chains of 2D nanosheets and alkyl chains of PAO6 offer long-term stable dispersion of 2D nanosheets in the PAO6, which ensures its basic qualifications as oil additives. The lubrication performance of the GO/g-C 3 N 4 nanocomposites as oil lubrication additive is evaluated utilizing GrC15/Ti-DLC friction pair. The outcomes demonstrate that the nanocomposites exhibit better lubricating qualities than single g-C 3 N 4 or GO. The oleophilic of the nanocomposites facilitates to visible surface adsorption and interlayer infiltration of oil molecules, allowing for decreasing the interlayer shear force. Furthermore, the creation of microscopic 2D heterogeneous layered structure through self-assembly stacking further diminishes the shear strength, leading to low friction in oil environment. From above, it is reasonable conclude that excellent performance of GO/g-C 3 N 4 nanocomposites on tribological properties of PAO6 oil is ascribed to synergistic effect between the g-C 3 N 4 and GO. Declarations Author Contributions All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The research was supported by Technology Youth Project of Chongqing Municipal Education Commission (Grant No.KJQN202303328). References Holmberg, K., Andersson, P., Erdemir, A. Global energy consumption due to friction in passenger cars. 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Synthesis of g-C3N4/Nb2O5 heterostructures and their application in the removal of organic pollutants under visible and ultraviolet irradiation. Ceramics International 43:3521-3530 (2017). Wang, F., Zhang, M., Li, J., Dong, Z., Xu, L., Wang, S., et al. Construction of 2D/2D graphene oxide/g-C3N4 hybrid for enhancing the friction and wear performance of poly (phthalazinone ether sulfone ketone). Polymer Composites 43:2055-2063 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3996457","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":275372979,"identity":"0c5c2cbb-154b-4773-960f-fc7bda08bb0f","order_by":0,"name":"Hongjiang Mou","email":"","orcid":"","institution":"Chongqing City Managment College","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hongjiang","middleName":"","lastName":"Mou","suffix":""},{"id":275372980,"identity":"734e19d3-1022-4c57-ad46-ed8d453cf17a","order_by":1,"name":"Wenqiu Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA10lEQVRIiWNgGAWjYLCCBAYbJN4B4rSkMfCQpoWB4TAJWgyO9x688bDtvL29RALjh7dtDHJ8NxIYPxfg03LmXLJFYtvtxB6JBGbJuW0MxpI3EpilZ+DRYnYjx0wCqCWBRyKBjZm3jSFxww0ggweflvtvQFrO2cO01BPWcoMHpOUAYw9US4IBIS32Z3KMLRLOJSf2nHnYLDnnnIThTCBDGp8WyfYzhjd/lNnZs7cnH/zwpsxGnu948sHP+LSAgASEYmwARo4EhEEISMBZhAwfBaNgFIyCkQkAo6xHMv3bYlUAAAAASUVORK5CYII=","orcid":"","institution":"Chongqing University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Wenqiu","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2024-02-28 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9","display":"","copyAsset":false,"role":"figure","size":315850,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEDS spectra of the wear scars of plates lubricated with (a) PAO6 base oil, (b) 0.04 wt% GO, (c) 0.04 wt% g-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e dispersions, and (d) 0.04 wt% GO/g-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e nanocomposite\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e 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GO/g-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e nanocomposite after friction.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3996457/v1/32182c2b2f5c80cb59591349.png"},{"id":51849451,"identity":"66762b40-3ae1-474c-a491-836013ac4e6d","added_by":"auto","created_at":"2024-03-01 08:36:26","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":169073,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCurve-fitted XPS spectra of (a) C1s, (b) O1s, (c) Fe2p, and (d) N1s of the wear scar of the plate lubricated by 0.04 wt% GO/g-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e nanocomposite-dispersions\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3996457/v1/426100ce3d263e869eee01ce.png"},{"id":51849520,"identity":"60e492a7-94a5-4c59-8c50-b386ee46acac","added_by":"auto","created_at":"2024-03-01 08:44:26","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":200224,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpeculated mechanisms of lubricating effect of GO/g-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eN\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e nanocomposites\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3996457/v1/c19ba2f5b1952fe8f930053d.png"},{"id":51929279,"identity":"5903e9e4-3ee0-49be-b011-0224448581d2","added_by":"auto","created_at":"2024-03-04 04:35:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3309192,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3996457/v1/71edea16-f459-44ee-90f7-48e23692e5a5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synergetic lubrication of Cross-Linked Nanocomposites and Enhanced the tribological performance of Ti-DLC film","fulltext":[{"header":"1.\tIntroduction","content":"\u003cp\u003eFriction\u0026nbsp;and\u0026nbsp;wear\u0026nbsp;lead to nonrenewable energy resource exhaustion and mechanical system invalidation[1].\u0026nbsp;\u0026nbsp;Friction and wear are major factors in a variety of applications, including microscale devices, bio-related devices like teeth and implants, and traditional bearings, pistons, and gears[2-5].\u0026nbsp;\u0026nbsp;Reducing oil consumption and related environmental pollution requires more efficient friction control ways. Employing a lubricant is the most efficient way to control or reduce wear and friction[6],\u0026nbsp;which was invented as early as 2400 BCE to move the heavy stones utilized for pyramid construction,\u0026nbsp;as described in ancient frescos in\u0026nbsp;Egyptians[7].\u0026nbsp;The most commonly used method is to add additives, which can form a mechanical film between friction components including reducing friction, anti-wear and corrosion. However, the old single lubrication additives with limitations contain environmental pollutants, and can\u0026rsquo;t adapt to a variety of working conditions. Therefore, the preparation of\u0026nbsp;environmentally friendly composite lubricant additive\u0026nbsp;with the simultaneous functions of friction reduction, anti-wear, and repair is\u0026nbsp;urgent to adapt to the current technological progress.2D nanomaterials have intensively shown excellent performance in tribology and lubrication due to layered structures[8]. High modulus and strength between monolayer, as well as low interlayer shear strength between neighboring layers, make them ideal for lubricating dual rubbing surfaces[9, 10].\u0026nbsp;In addition, 2D nanomaterials have a significantly higher specific surface area, allowing them to cover a larger surface area when absorbed on the substrate surface, limiting direct contact with friction surfaces[11].\u003c/p\u003e\n\u003cp\u003eGraphitic carbon nitrogen (g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e)[12, 13]\u0026nbsp;has garnered plenty attention recently. The layered structure of\u0026nbsp;g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e consists of tri-striazine units (as the basic building block),\u0026nbsp;which are\u0026nbsp;joined with tertiary amino groups. Weak van der Waals forces allow the sheets of\u0026nbsp;g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e to interact with one another to form bulk\u0026nbsp;g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e materials[14].\u0026nbsp;\u0026nbsp;It has great thermal and chemical\u0026nbsp;stability[15]\u0026nbsp;and high mechanical properties\u0026nbsp;(elastic modulus 320 GPa and hardness 25 GPa)[16], all of which make it a promising candidate for a revolution green lubricant additive.\u0026nbsp;In addition, this kind of nanomaterial does not contain metal elements, has good biocompatibility and low toxicity, and has good application prospects in the field of biological detection[17]. However, the tribological performances of single g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanomaterial are not enough. Modification technology based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanomaterial is time-consuming and cumbersome, and the efficiency needs to be further improved.\u0026nbsp;Therefore, modification of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanomaterials construct materials with excellent lubrication properties according to practical application requirements. It will be the key to the promotion and application of this material in the field of friction lubrication.\u003c/p\u003e\n\u003cp\u003eGraphene,\u0026nbsp;an emerging 2D nanomaterial,\u0026nbsp;has gained popularity for its exceptional properties, such as high electron mobility, high Young\u0026apos;s modulus (~1 TPa), remarkable thermal conductivity, excellent electrical conductivity, and optical transparency. The microscopic and macroscopic tribological behaviors of graphene have been investigated by the academic community since discovered in 2004, it has shown an alluring prospect as a green lubrication additive[18].\u0026nbsp;The flakes move quickly until they reach a new commensurate location on the microscale, which is caused by a tip-induced change from a commensurate to an incommensurate registry with the underlying graphene layer (the superlubric state)[19].\u0026nbsp;On the macro-scale, ultrafine particles resembling miniaturized crumpled paper balls as a high-performance additive could self-disperse in oil and act like nanoscale ball bearings to reduce friction and wear and significantly improve the lubrication properties of polyalphaolefin base oil[20].\u003c/p\u003e\n\u003cp\u003eNanocomposites\u0026nbsp;composed of two nanomaterials could\u0026nbsp;typically generate effects that\u0026nbsp;are not possible with a single nanomaterial.\u0026nbsp;Taking the combination of\u0026nbsp;0D and 2D nanomaterials,\u0026nbsp;the\u0026nbsp;pathway of nano diamond and graphene was proposed to improve the tribological properties of hydrogenated amorphous carbon (a-C: H) in ambient\u0026nbsp;air[21].\u0026nbsp;In-situ growth of nanostructured tribo-layers determines the bonding characteristic of a-C: H film and the tribo-induced structural evolution of lubricants.\u0026nbsp;Interlayer friction of heterostructures achieves superlubricity properties by means of interlayer couplings[22]. The hydrophilization of\u0026nbsp;the BP-GO hybrid nanomaterials\u0026nbsp;makes it easier for water molecules to adsorb on surfaces and penetrate between layers[23].\u0026nbsp;The unique heterojunction stacking structure further reduced the shear strength,\u0026nbsp;endowed\u0026nbsp;the fascinating prospect of the lubricating properties\u0026nbsp;of DLC.\u0026nbsp;Graphene and MoS\u003csub\u003e2\u003c/sub\u003e composites could provide low friction and\u0026nbsp;wear between DLC and steel[24].\u0026nbsp;At\u0026nbsp;the frictional interface, MoS\u003csub\u003e2\u003c/sub\u003e was dissolved into Mo and\u0026nbsp;S at high contact pressure. It is contributed to convert the\u0026nbsp;DLC into amorphous carbon and graphene, which provides a low\u0026nbsp;shear sliding and results in low friction and wear.\u0026nbsp;Experimental and theoretical simulations have confirmed that the lateral interactions between two incommensurate contacting surfaces of graphene and hexagonal boron nitride (h-BN) could be effectively counteracted to achieve a robust heterojunction, resulting in ultralow sliding friction[25-27].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe above discussions in the experiments and theory have verified that 2D nanocomposites, by forming van der Waals heterojunctions and disproportional contact, can efficiently minimize friction and energy dissipation.\u0026nbsp;However, achieving\u0026nbsp;low wear\u0026nbsp;and low friction by using 2D\u0026nbsp;nanocomposites\u0026nbsp;in oil remains a major challenge to overcome.\u0026nbsp;Therefore, further exploration of the way to make DLC less friction and wear in oil-based lubrication environments is still needed. In this work,\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites were successfully synthesized by the self-assembly method, and the oil dispersion stability of two-dimensional nanomaterials was modified by octadecyl amine. The tribological performance of 2D nanocomposite as a lubricant was evaluated by contacting GrC15/ Ti-DLC friction pair. In the subsequent step, the lubrication mechanism of the nanocomposite and Ti-DLC film was discussed based on the experimental results.\u0026nbsp;\u003c/p\u003e"},{"header":"2 Experiment details","content":"\u003ch2\u003e\u003cstrong\u003e2.1\u0026nbsp;Materials\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe graphene oxide powder (GO, 99%),\u0026nbsp;N-methyl\u0026nbsp;pyrrolidone (NMP,\u0026nbsp;\u0026ge;99.5%) and octadecylamine were suppliers by Shanghai Aladdin Biochemical Technology Co.,\u0026nbsp;Ltd. The\u0026nbsp;The pyrolysis of urea in a muffle furnace produced the\u0026nbsp;g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets using the following procedure: First, heat 100 g of urea in an alumina crucible for 40 minutes at a rate of\u0026nbsp;4\u0026nbsp;\u0026deg;C/min.\u0026nbsp;Next,\u0026nbsp;increase the temperature\u0026nbsp;to 560\u0026nbsp;\u0026deg;C at rate of 2\u0026nbsp;\u0026deg;C/min and holding for 100 min. the obtained buck g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e was collected into weighing bottle, after a\u0026nbsp;natural cooling process. Anhydrous ethanol (99.7%) originated from Tianjin Bohua Pharmaceutical Chemical Co., Ltd., China.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003e2.2\u003c/strong\u003e \u003cstrong\u003eSynthesis of\u0026nbsp;\u003c/strong\u003eGO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e \u003cstrong\u003eO Nanocomposites\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eNMP is\u0026nbsp;an excellent organic solvent[28]\u0026nbsp;to exfoliate 2D material, and it has been\u0026nbsp;demonstrated that a saturated NMP solution could increase the stability of the prepared 2D nanosheets[29]. The presence of NMP solution has no effect on the structure or morphology, 200 mL\u0026nbsp;of NMP solution was mixed with 60 mg of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and\u0026nbsp;GO powder, and ultrasonic exfoliation was then performed for 4 hours in ice water bath kepting below 30\u0026nbsp;\u0026deg;C. The\u0026nbsp;mixture nanosheets dispersion was centrifuged at 9000 rmp min\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e for 10 min after ultrasonic exfoliation, to generate a mixture nanosheets dispersion.\u0026nbsp;The\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite\u0026nbsp;was obtained via washing the leftover NMP in\u0026nbsp;absolute ethanol.\u0026nbsp;Since there were no chemical interactions during this self-assembling process, the main driven force that combined g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e with GO was the van der Waals force. It is well known that\u0026nbsp;inorganic nanoparticles are poor dispersion stability in organic liquids, thus requiring the same concentration of surfactant to improve dispersion. Octadecylamine was utilized as a dispersing agent. In the subsequent step, the ethanol dispersion of the octadecylamine (2mg/mL\u003csup\u003e-1\u003c/sup\u003e) was added drop-wise into the anhydrous ethanol dispersion of the\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites while stirring continuously at 800 rpm and the\u0026nbsp;temperature of 70\u0026deg;. The reaction mixture was then refluxed for 24 hours. The\u0026nbsp;octadecylamine-modified\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites were thoroughly washed with ethanol and then separated by vacuum filtration using a membrane filter. The washing and filtration were repeated four times to obtain the modified\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite.\u0026nbsp;The single\u0026nbsp;g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO were modified\u0026nbsp;with same way.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003e2.3 \u003cstrong\u003eDispersion stability test of Modified Nanocomposites\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eIn order to investigate the dispersion stability of composite nanomaterials in PAO6, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, GO\u0026nbsp;and GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e were\u0026nbsp;ultrasonically\u0026nbsp;dispersed into PAO6 for 30min,\u0026nbsp;respectively. To prepare dispersion of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/GO nanocomposite, firstly the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO oil dispersions were prepared by mechanical depolymerisation process, respectively.\u0026nbsp;In the process, 0.01 wt%, 0.02 wt%, 0.04 wt%, 0.06 wt%, 0.08 wt% and 0.1 wt% of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO powders were dispersed in PAO6,\u0026nbsp;respectively. Subsequently, the 0.04 wt% g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/GO nanocomposite dispersion was ultrasound for 20 min, utilizing an ultrasonic probe (Branson Digital Sonifer 450, USA) at a power\u0026nbsp;of 400 watts for 10 min with a 10s on/off interval.\u0026nbsp;\u0026nbsp;\u003cstrong\u003eFigure 1\u003c/strong\u003e depicts dispersion results after\u0026nbsp;sonication and 7 days of undisturbed ambient air.\u0026nbsp;The dispersion test reveal that nanosheets modified with octadecamine effectively disperse in PAO6 oil, PAO6 base oil was also employed as a baseline for comparison. The long-term dispersion stability of modified nanosheets was attributed to their high specific surface area along with presence of ample alkyl chains. The van der Waals interaction between the octadecyl chains of modified nanosheets and alkyl chains of PAO6 oil causes nanosheets to\u0026nbsp;distribute completely\u0026nbsp;and ensure long term stability.\u0026nbsp;The high specific surface area and abundance of alkyl chains were responsible for\u0026nbsp;the long-term dispersion stability of modified nanosheets.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cem\u003e2.4 Characterization\u003c/em\u003e\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe size distributions of the GO, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites, were measured by a particle analyzer (Litesizer 500). Transmission electron microscopy (TEM, TecnaiG2 TF20) combined energy dispersive X-ray (EDX) microanalysis and field emission scanning electron microscopy (FESEM, JSM 6701F) were carried out to determine morphology and elements of product. A TEM microgate with a carbon support film was utilized as a carrier for the prepared nanomaterial. Scanning electron microscopy (SEM, TESCAN, MIRA3) equipped with energy dispersive spectroscopy (EDS, XFlash 6130, Bruker) was used to observed the morphology of wear tracks and wear scars and distribution \u003ca href=\"javascript%3A;\"\u003eof\u003c/a\u003e elements. A X-ray photoelectron spectra (XPS, ESCALAB 250Xi.) was employed to record the chemical compositions and chemical bonding in the wear scar. The X-ray diffraction patterns (XRD) were recorded by an EMPYREAN.\u003c/p\u003e\n\u003ch2\u003e2.5 Tribological tests\u0026nbsp;\u003cstrong\u003e\u003cem\u003eof GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/em\u003e\u003c/strong\u003e \u003cstrong\u003e\u003cem\u003enanocomposites\u003c/em\u003e\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eTribological tests ofTi-DLC film subjected to lubricated sliding against GrC15 ball with a diameter of 10 mmwere carried out on a UMT-TriboLab (Bruker. US) in ball-on-disc reciprocating mode sliding for 1.44 km. All the tests were conducted at ambient temperature with amplitude of 2 mm, sliding frequency of 10 Hz, a sliding time of 1h and a normal load of 200 N which corresponded to a maximum Hertzian contact pressure of approximately \u0026sim;1.6 GPa. A microsyringe was used to drop 50 \u0026mu;l of lubricant into the contact region after the lubricant had been ultrasonically mixed for 0.5 hours to create a stable and uniform suspension. All the disks and dual balls had been ultrasonically degreased with ethanol to remove contaminants before each test. \u0026nbsp;Following friction tests, the worn surfaces and dual balls were cleansed by acetone. A non-contact three-dimensional (3D) surface profiler (MicroXAM-800, KLA-Tencor, USA) was employed to calculate the wear loss of each wear track at five randomly locations.\u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003ch2\u003e3.1 \u003cstrong\u003eChemical and Structural of the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e \u003cstrong\u003enanocomposites\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe size distribution of GO, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites was examine by a particle analyzer in \u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e. The results showed that GO nanosheets ranged from about 590 to 1120 nm (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e2a\u003c/strong\u003e), while g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets was concentrated around 290-650 nm (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e2b\u003c/strong\u003e). Particle sizes in the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites range from 200 to 1216 nm (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e2c\u003c/strong\u003e), indicating that the friction process has no effect on one another\u0026rsquo;s structure or size. \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 3\u003c/strong\u003e presents the fine microstructure and SAED patterns of GO, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4 \u003c/sub\u003eand\u003csub\u003e \u003c/sub\u003eGO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites. \u003cstrong\u003eFigure 3a \u003c/strong\u003eillustrates how GO nanosheets with a handful of layers are usually crinkled and entangled in in a few square micrometers areas. Selected area electron diffraction (SAED) images demonstrate clearly defined diffraction rings, indicating that the GO nanosheets have a crystalline and well-ordered structure. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003enoosheets display an individual layer or stack of many layers, like a typical agglomeration in \u003cstrong\u003eFigure 3b\u003c/strong\u003e. More importantly, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets have a smaller size than GO nanosheets. \u003cstrong\u003eFigure 3c\u003c/strong\u003e shows that the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite has numerous g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets decorated on the surface of GO. The particles size of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets is about 543 nm, while the particles size of GO nanosheets is approximately 959 nm, which is consistent with the size distribution in \u003cstrong\u003eFigure 2\u003c/strong\u003e. Meanwhile, EDX analysis is further confirmed that the formation of GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite appear strong intensity peaks corresponding to N element (\u003cstrong\u003eFigure 3d\u003c/strong\u003e). A small amount of O elements may be caused by graphene oxidation. These findings collectively verify that GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets coexist in the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e heterostructure. \u003c/p\u003e\n\u003cp\u003eFurthermore, FESEM revealed the microstructure of the GO, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4 \u003c/sub\u003eand\u003csub\u003e \u003c/sub\u003eGO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites. \u003cstrong\u003eFigure. 4a\u003c/strong\u003e reveals that GO has a few-layered and wrinkled structure. The size distribution of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets is small than GO (about 400 nm) in \u003cstrong\u003eFigure. 4b\u003c/strong\u003e. Several minute particles of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e load on the surfaces of GO, resulting in a layer-by-layer hybrid structure of GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e in \u003cstrong\u003eFigure 4c\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eXRD diffraction peaks of the GO, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4 \u003c/sub\u003eand\u003csub\u003e \u003c/sub\u003eg-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/ GO nanocomposites were investigated to explore the structural alterations in \u003cstrong\u003eFigure 5\u003c/strong\u003e. The (100) peak of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e at 13.1\u0026deg; corresponds to the in-plane structural packing of nitrogen-linked heptazine units with a lattice distance of 0.676 nm. The (002) peak at 27.5\u0026deg; indicates aromatic graphite lattices with an interplanar stacking distance of 0.324 nm[30, 31].The characteristic peak of GO, C (002), appears at 21\u0026deg;, indicating a smaller interlayer spacing of 0.41nm, approximately. This is significantly larger than characteristic interlayer spacing of graphene (0.34 nm)[32, 33]. This indicates that the oxygen function has vanished on the basal planes of the alkylated GO nanosheets. At this stage, weak van der Waals contacts can join the lamellas of alkylated GO nanosheets since the sp2 carbon skeleton fails to contain any oxygen functionalities[33]. In GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites, the unbroken GO structure is represented by the peak at 21\u0026deg;, while the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e structure is indicated by the peak at 27\u0026deg;, indicating that the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e decorating on the surface of the GO nanosheets are not affect each other. The peak of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e at 13.1\u0026deg;vanished because decreases of in-plane structure accumulation. This might result from the GO nanosheet combination; intercalation structure could emerge. \u003c/p\u003e\n\u003ch2\u003e3.2 \u003cstrong\u003e\u003cem\u003eTribological Properties of the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/em\u003e\u003c/strong\u003e \u003cstrong\u003e\u003cem\u003enanocomposites\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e as Lubricant Additives\u003c/em\u003e\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe lubrication properties of GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e were investigated independently. \u003cstrong\u003eFigure 6a\u003c/strong\u003e and \u003cstrong\u003e6b\u003c/strong\u003e displays the average coefficient of friction (COF)and wear rate of wear scar when lubricated with varying concentrations of GO-dispersion and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e- dispersion, separately. PAO6 is 0 wt% as comparison. \u003cstrong\u003eFigure 6a \u003c/strong\u003eshows that as concentrations increased, the COF and wear rate first decreased and then reached a minimum at 0.04 wt%. From there, as concentrations increased further, the COF increased while the wear rate remained essentially unchanged. At the optimal concentrations, the wear rate decreased by approximately 85.8% and the COF decreased by around 20%, from 0.1 to 0.08, in comparison to PAO6. The average COF and matching wear rates of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersions at various concentrations are displayed in \u003cstrong\u003eFigure 6b\u003c/strong\u003e. Similar variations trend emerged, the lowest COF and wear rate appear at 0.04 wt% and 0.06 wt%, and lowered by 10% and 83% comparing to PAO6, respectively. The optimal concentration of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e is considered to be in the range 0.04-0.06 wt%. It is impossible to ignore that the optimal concentration of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersion is considerably higher than GO-dispersions, which is most likely because of smaller particles size and better dispersion of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e. In summary, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersions and GO-dispersions may provide excellent lubrication performance at concentrations ranging from 0.04 to 0.06wt%. When the concentration was relatively low, effective lubricating films could not be formed because insufficient nanosheets could enter the contact area, so COF and wear rate decreased with the increase of concentration. Nevertheless, overabundance of nanosheets might lead to unstable dispersion and rather massive agglomerates, which will exacerbate wear. \u003c/p\u003e\n\u003cp\u003eBased on the above experimental results, 0.04 wt% concentration was chosen as the optimal concentration to investigate the lubricant mechanisms of GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites. Friction coefficients and wear rates of three lubricants were shown in \u003cstrong\u003eFigure 7\u003c/strong\u003e. Obviously, the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersions exhibits the most wonderful potential; its friction coefficient and wear rate were approximately reduced by 18% and 89.9%, respectively, compared with control of pure PAO6. The lubricant properties of GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite are superior to those of GO or g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e alone. Outstanding anti-friction and anti-wear effect of GO/ g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e may originate from the synergistic lubrication action of the two units. \u003c/p\u003e\n\u003ch2\u003e3.3 Wear surface analysis\u003c/h2\u003e\n\u003cp\u003e\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e8 \u003c/strong\u003eexhibits the SEM images of wear scars and wear tracks of Ti-DLC under the load of 200N, and the boundary of the wear scar and wear track was marked with white line. Under PAO6 lubrication conditions (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e8a and 8b\u003c/strong\u003e), the wear scar area is broad and the wear tracks has furrows and scratches that displayed with an evidence of complete film failure. Under g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e dispersion lubrication condition (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e8c and 8d\u003c/strong\u003e), Certain scattered bright spots appeared on the wear surface, indicating damage in some areas of film, nonetheless the area of wear scar is smaller than that of PAO6. While GO (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e8e and 8f\u003c/strong\u003e) and GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e (\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e8g and 8h\u003c/strong\u003e) dispersion lubrication conditions, the wear tracks displayed entire film, smallest wear scar diameter, and the shallowest pear ditch. Only a faint rim of the contact area can be observable. The ball and film inside white rim appear clean and similar to the outside region. Therefore, GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites combining the anti-wear property of GO and the anti-friction peculiarity of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, fully demonstrate their advantages in oil lubrication environments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e9\u003c/strong\u003e illustrates the elemental distribution in the wear scars on the steel ball. The wear scar generated with the POA6 exhibited the lowest C content, a small quantity of Ti content, and a strong peak of Fe in \u003cstrong\u003eFigure 9(a), \u003c/strong\u003ewhere Fe originating from the steel ball, C regarding the steel ball and Ti-DLC film, and Ti over the Ti-DLC film. The outcome suggests that the transferred material was mainly from the Ti-DLC film. The wear scar lubricated with GO dispersion appeared a strong peak for C in \u003cstrong\u003eFigure 9(b)\u003c/strong\u003e, indicating that the GO layers adsorbed on the contact interfaces. Besides C, Fe and Ti elements, it determines a mass of N elements (3.17 at%) in the wear scar \u003cstrong\u003eFigure 9(c)\u003c/strong\u003e. These elements are obviously from the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e additives, indicating that the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets transferred to surrounding area. Additionally, peaks of Fe, Ti and O as well as relatively high concentrations of C and N appeared in \u003cstrong\u003eFigure 9(d)\u003c/strong\u003e when the wear scar lubricated with the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersions. Which indicated that g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO nanosheets might be in charge of the enhanced tribological performance by transferring to the contact area and forming a lubricating film around synergy with the Ti-DLC film.\u003c/p\u003e\n\u003cp\u003eTo investigate the particle size changes of additives after the lubrication experiments, the particle sizes distribution of GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets were measured utilizing same particle analyzer in \u003cstrong\u003eFigure\u003c/strong\u003e \u003cstrong\u003e10\u003c/strong\u003e. The particle sizes of GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4 \u003c/sub\u003ebecome smaller than those before friction test in \u003cstrong\u003eFigure\u003c/strong\u003e \u003cstrong\u003e2\u003c/strong\u003e. This indicates that the flake additives were triturated during the friction process. Nevertheless, the morphology of the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposite was preserved from grinding to an extent when GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e were employed in combination.\u003c/p\u003e\n\u003cp\u003eCurve-fitted XPS spectra of C1s, O1s, Fe2p, and N1s on the wear scar lubricated with 0.04 wt% GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-dispersions illustrated in \u003cstrong\u003eFigure \u003c/strong\u003e\u003cstrong\u003e11\u003c/strong\u003e.\u003cstrong\u003e Figure \u003c/strong\u003e\u003cstrong\u003e11\u003c/strong\u003e\u003cstrong\u003ea \u003c/strong\u003eillustrates that the C-C peak at 284.5 eV reflects amorphous carbon, which form by GO and the deposition of Ti-DLC film. The peaks at 286.5 eV and 288.2 eV are assigned to the C-N, N-C-N backbone in the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e respectively[34]. In\u003cstrong\u003eFigure 11b,\u003c/strong\u003e the O1s peak at 532.1 eV was indexed to hydroxides, indicated that adsorbed film derived from the GO or/and organics containing hydroxides. In \u003cstrong\u003eFigure 11c\u003c/strong\u003e, the Fe\u003csub\u003e2p\u003c/sub\u003e of the Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e groups was represented by the Fe\u003csub\u003e2\u003c/sub\u003ep\u003csub\u003e3/2 \u003c/sub\u003eand Fe\u003csub\u003e2\u003c/sub\u003ep\u003csub\u003e1/2\u003c/sub\u003e peaks ,which were located at binding energies of 711.1 and 724.7 eV[35], respectively. These results verify that the total prevention of the tribo-oxidation is not possible. In \u003cstrong\u003eFigure 11d\u003c/strong\u003e, N 1s spectrum with two fitting peaks at 398.7 eV and 400.5 eV were ascribed to N-C=N group of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and the nitrogen in tertiary N -C3 group of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e[36]. Therefore, it is reasonable to assume that the GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e of the nanocomposites was deposited on the contact surfaces, where it formed a physical protective film which served as a barrier during the rubbing process. \u003c/p\u003e\n\u003ch2\u003e3.4 Discussion on lubrication mechanism \u003c/h2\u003e\n\u003cp\u003eBased on the above analysis, in\u003cstrong\u003e Figure 12\u003c/strong\u003e vividly summarized the speculated mechanism for the excellent performance of GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites as additives sliding against Ti-DLC film. The GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites was modified with octadecylamine during the synthesis process, which results in adsorbed alkyl chain on the surfaces of the 2D nanosheets. The synthesized GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites uniformly and stably dispersed in PAO6 oil, guaranteeing the continuous supply of additives to the contact surface during the sliding process. The dangling bonds on the surface of the Ti-DLC film may be passivated by the organic chain adsorbed on the GO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e surfaces, which would encourage the decrease of friction.\u003c/p\u003e\n\u003cp\u003eAdditionally, the modified GO/ g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e has the ability to absorb oil molecules from the surface and penetrate between layers, which helps to decrease the interlayer shear stress, thicken the oil film, and keep friction pairs from coming into direct contact. \u003c/p\u003e\n\u003cp\u003eAs g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e and GO are typical 2D layered materials with very low inter-laminar shear strengths, GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites form a 2D van der Waals heterojunction microscopically through self-assembly. The shear strength is further reduced because the lattice mismatch. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets are easily to deposit on micro-pits and repair the contact surface because of their extremely small size (Figure 2). Figure 11 indicated that a few GO nanosheets may be distorted and ruptured because of friction force and heat after a period of sliding time. And then g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets are exposed and released. In addition, to bear the load and separate the friction surface, the released g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets can prevent GO from grinding and repair the ruptured film, thereby extending the durability of the deposition film. Since the high contact pressure creates stressed zones of traction and compression, they produced a thin physical lubricating film on the Ti-DLC film. It\u0026rsquo;s special layered stacking structure helps the two contact surfaces slide, resulting in low friction behavior. The lubricating film that forms will keep the two contact surfaces from coming into direct contact during the sliding process. Last but not the least, the excellent thermal resistance of the composites can reduce the friction heat and shield them from the damaging effects of high temperature, which results in the remarkable tribological properties[37].\u003c/p\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eIn this work,\u0026nbsp;the\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites\u0026nbsp;are successfully synthesized utilizing self-assembly.\u0026nbsp;Alkylated graphene, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand\u003csub\u003e\u0026nbsp;\u003c/sub\u003eGO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites\u0026nbsp;nanosheets could thoroughly disperse in the PAO6 oil. The van der waals interaction between octadecyl chains of 2D nanosheets and alkyl chains of PAO6 offer long-term stable dispersion of 2D nanosheets in the PAO6, which ensures its basic qualifications as oil\u0026nbsp;additives.\u0026nbsp;The lubrication performance of the\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites\u0026nbsp;as oil lubrication additive is evaluated utilizing GrC15/Ti-DLC friction pair. The outcomes\u0026nbsp;demonstrate\u0026nbsp;that the\u0026nbsp;nanocomposites\u0026nbsp;exhibit better lubricating qualities than single g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eor GO. The oleophilic of the\u0026nbsp;nanocomposites\u0026nbsp;facilitates\u0026nbsp;to visible surface adsorption and interlayer infiltration of\u0026nbsp;oil molecules, allowing for\u0026nbsp;decreasing\u0026nbsp;the interlayer\u0026nbsp;shear force.\u0026nbsp;Furthermore, the\u0026nbsp;creation\u0026nbsp;of microscopic 2D heterogeneous layered structure through self-assembly stacking further\u0026nbsp;diminishes\u0026nbsp;the shear strength, leading to low friction in\u0026nbsp;oil environment.\u0026nbsp;From above,\u0026ensp;it is reasonable\u0026ensp;conclude\u0026ensp;that\u0026nbsp;excellent performance of\u0026nbsp;GO/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanocomposites\u0026nbsp;on tribological properties of PAO6 oil is ascribed to synergistic effect between the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand GO.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003cstrong\u003e\u003cbr\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have given approval to the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eACKNOWLEDGMENT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research was supported by Technology Youth Project of Chongqing Municipal Education Commission (Grant No.KJQN202303328).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHolmberg, K., Andersson, P., Erdemir, A. 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Polymer Composites 43:2055-2063 (2022).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"graphene oxide, graphitic carbon-nitrogen, Ti-DLC, oil lubricant additives, tribological performance","lastPublishedDoi":"10.21203/rs.3.rs-3996457/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3996457/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Two-dimensional(2D) nanocomposites exhibit theoretically and experimentally considerable promise for lowering friction and dissipating energy in dry sliding. However, a significant obstacle still stands in lower friction by introducing the 2D nanocomposites in oil lubrication environment. Here, g-C3N4/GO nanocomposites with a 2D layered structure were synthesized successfully. Ti-DLC film was used to examine the tribological performance of graphene oxide (GO), graphitic carbon nitride (g-C3N4), and carbon nitride/graphene oxide (GO/g-C3N4) nanocomposites in oil. As lubrication additives, the friction-reducing and anti-wear properties of GO/g-C3N4 nanocomposites were superior than a single nanomaterial of GO or g-C3N4 nanosheets. The synergistic lubricating effect involves the easy interlayer shear resulting from the oleophilic and distinct microscopic heterojunction stacking structure of the GO/g-C3N4 nanocomposites. This led to the formation of an adsorption lubrication film containing PAO6, g-C3N4, and GO. These innovative investigations have demonstrated that adding 2D GO/g-C3N4 nanocomposites into PAO6 is an intriguing approach to improving the dependability and energy efficiency of current mechanical systems.","manuscriptTitle":"Synergetic lubrication of Cross-Linked Nanocomposites and Enhanced the tribological performance of Ti-DLC film","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-01 08:36:21","doi":"10.21203/rs.3.rs-3996457/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f9b75753-8fcb-48ca-836d-aae14c327cfd","owner":[],"postedDate":"March 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-04T04:34:39+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-01 08:36:21","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3996457","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3996457","identity":"rs-3996457","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}