Interactions Balancing Competition and Cooperation between Covalent-Organic Framework Additives and PEG Base Oil toward Advanced Lubrication

The Study of the Inhibitive Behavior of COF-5 Lubricant Additives on Wear and Corrosion of the Tin Bronze Friction Pair during the Current-Carrying Process

COF-5 is an excellent choice as a lubricant additive due to its high specific surface area and regular layer stacking structure. In this paper, the porous covalent organic frameworks of the COF-5 nanomaterial were successfully synthesized as a lubricant additive via a method of sonochemical synthesis. Pure [BMIM][SCN] (BS) was used as the base oil, and the tribological properties of the COF-5-BS composite lubricant were evaluated by using a ball-on-disk wear tester. The results were demonstrated that the wear volume of BS with the addition of 0.1 wt % COF-5 was reduced by 46.64% as compared to that of the pure BS, and the corrosion on the friction interface was effectively inhibited by the addition of COF-5 nanomaterial. This phenomenon was ascribed to COF-5 with a large specific surface area, being adsorbed onto the friction interface, which could repair the wear-induced pits and prevent the direct contact between the metal substrate and the corrosive medium. The tribological properties of the COF-5-BS composite lubricant could be efficiently regulated under the applied electric current. The results of intelligent electric current-controlled friction were indicated that the average coefficients of friction (COF) under the current stimulation of 30 mA with on/off cycling were reduced by 12.05% as compared to that of a continuous current operated for 1 h. Moreover, the wear volume and depth were reduced by 11.69% and 8.75%, respectively. That is because the short duration of current regulation could enhance the rapid formation of a lubricant film composed of BS liquid and COF-5 nanosheets on the friction interface. Meanwhile, the temperature on the interface would not be high to produce the failure of lubricating film, resulting in an excellent low friction coefficient and excellent antifriction property.

Fabrication of Ag Nanoparticle-Embedded Covalent Organic Frameworks for Oil Gel with Long-Term Stability and High Lubrication Performance

In previous reports, covalent organic frameworks (COFs) have demonstrated significant potential as lubricant additives. Herein, we embedded Ag nanoparticles in the DT-COF (polycondensation polymer of 2,5-dihydroxyterephthalaldehyde and 4,4',4″-(1,3,5-triazine-2,4,6-triyl) trianiline) matrix via the ball milling method and utilized this composite (Ag@DT-COF) as an additive for supermolecule oil gel. The low molecular weight gelator effectively mitigates the dispersion challenges of COFs in lubricant oil, while the embedded Ag nanoparticles enhance the repairing effect and antipressure performance of the lubricant. The resulting Ag@DT-COF gel exhibits a reduction in the average friction coefficient and wear volume of base oil by 46.0% and 87.5%, respectively, and increases the load-carrying capacity to 750 N. The remarkable tribological properties are attributed to the easy adsorption of DT-COF, antiwear characteristic of Ag nanoparticles, and the gelator that ensures the long-term stability of oil gel.

Covalent-Organic Framework Nanomaterials: Energy Band Engineering Generating Ultrathin Lubrication Films for Excellent Lubrication

It is, in fact, inevitable for steel to be covered with a layer of iron oxides and/or peroxides on its surface. However, knowledge of its existence and functionality for tribological behaviors is usually ignored. Herein, covalent-organic framework nanomaterials (CONs) composed of three well-screened acceptors and a donor through the imide linkage were fabricated to explore their lubrication performances. The results indicate that the energy-level matching between CONs and iron oxides or peroxides leads to the formation of a Z-scheme heterojunction structure at the rubbing interface. Also, the friction produces an internal electric field in the heterojunction, which drives the negative atomic/ionic species from the sliding interface to immigrate into the pore of CONs and resettle inside to engender the pinning effects, producing a fixed lubrication layer. Synchronously, it also attracts the free CONs in the base oil to form an easy-shear lubrication layer assembling onto the fixed one, producing a lubrication film with two layered configurations. Finally, the unique lubrication film, despite its thickness of a dozen nanometers, still exhibits impressive friction reduction and antiwear. This finding will inspire the technology to utilize the intrinsic surface nature of steel materials to exploit lubricant additives or modulate tribological behaviors.

Mechanochemical Synthesis of Thiadiazole Functionalized COF as Oil-Based Lubricant Additive for Reducing Friction and Wear

In this work, the functionalized covalent organic framework (COF) was prepared via a convenient ball milling process. The aldehyde group terminated COF-F reacted with amino thiadiazole in the ball milling jar under mechanical forces; hence, the thiadiazole functionalized COF-F was obtained and denoted as Thdz@COF-F. The as-prepared Thdz@COF-F serves as an oil-based lubricant additive and exhibits remarkable tribological properties, which can reduce the average friction coefficient of base oil from 0.169 to 0.102 and decrease the wear volume by 87.0%. The antifriction and antiwear performances are mainly due to the repairing effect of Thdz@COF-F nanoparticles and the protective tribo-film that averts the direct contact of friction pairs. In addition, through the ball milling method, triazole and thiazole functionalized COF-F were also prepared and represented good lubrication performance, demonstrating the feasibility of this mechanochemical synthesis method for functionalized COFs.