Oleic acid (OA) modified ZnO nanoparticles with an average size of 4.04 nm were prepared via a facile in situ one-step route. The as-prepared ZnO nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The light-absorbing performance and thermal stability of the as-prepared ZnO nanoparticles were evaluated by ultraviolet-visible light spectrophotometry and thermogravimetric analysis, and their tribological behaviour as the lubricant additive in poly-alpha olefin (PAO) and diisooctyl sebacate (DIOS) base oils was evaluated with a four-ball machine. The surface morphology of the wear scar was observed with a scanning electron microscope and a three-dimensional optical profiler, and the element composition of the wear scar was determined by energy dispersive spectrometry. It was found that the surface-capping of ZnO nanoparticles by OA helps to greatly increase their dispersibility and thermal stability. In the meantime, OA-modified ZnO nanoparticles can effectively improve the antiwear and friction-reducing abilities as well as the load-carrying capacity of the base oils, which is due to the formation of a tribofilm in association with the tribo-sintering and/or adsorption of the additives on the rubbed steel surfaces. Furthermore, the friction-reducing and antiwear performances of the as-prepared ZnO nanoparticles as lubricating oil additives seem to be closely related to the polarity of the base oils. Namely, the OA-modified ZnO additive exhibits better tribological behaviour in apolar PAO than in polar DIOS.

CeO₂ nanoparticles are potential anti-wear additives because of their outstanding anti-wear and load-bearing capacity. However, the shear-sintering tribo-film formation mechanism of oxide nanoparticles limits the tribo-film formation rate and thickness greatly. In this study, by compounding with zinc dioctyl dithiophosphate (ZDDP), ultra-fine CeO₂ nanoparticles modified with oleylamine (OM) can quickly form 2 µm ultra-thick tribo-film, which is 10–15 times thicker than that of ZDDP and CeO₂, respectively. The ultra-thick tribo-film presents a nanocomposite structure with amorphous phosphate as binder and nano-CeO₂ as filling phase, which leads to the highest loading capacity of composite additives. The results of adsorption experiments tested by dissipative quartz crystal microbalance (QCM-D) showed that the P_B value of additive has nothing to do with its equilibrium adsorption mass, but is directly proportional to its adsorption rate in 10 s. The compound additive of CeO₂ and ZDDP presented the co-deposition mode of ZDDP monolayer rigid adsorption and CeO₂ viscoelastic adsorption on the metal surface, which showed the highest adsorption rate in 10 s. It is found that the tribo-film must have high film forming rate and wear resistance at the same time in order to achieve super thickness. Cerium phosphate was formed from ZDDP and CeO₂ through tribochemistry reaction, which promotes the formation of an ultra-thick tribo-film with nanocomposite structure, which not only maintains the low friction characteristics of CeO₂, but also realizes high P_B and high load-carrying capacity.

In the contemporary pursuit of ensuring long-term lubrication for transmission units operating under harsh conditions, significant challenges remain. Researchers have been investigating porous polymer materials as a potential solution; however, achieving exceptionally low friction and wear has proven elusive. To address this issue, we have developed a novel porous fluorinated polyimide (PPIF-250) characterized by superior mechanical performance, heat resistance, and higher oil content and retention compared to other PPIs with comparable pore size and porosity. Extensive lubrication testing under varying conditions has demonstrated that PPIF-250 achieves remarkably low friction and wear characteristics, even under high FV values, representing a significant advancement in this field. Furthermore, our findings indicate that the polarity of base oils plays a crucial role in determining the oil content and retention of PPIF-250. Specifically, the integration of PPIF-250 with a tailored PEG-200 structure results in significantly improved oil content, retention, and long-term lubrication relative to other base oils. This improvement is attributed to the formation of high-load capacity boundary films within the PPIF-250 matrix, comprising oxidation processes involving carboxyl functional groups that chelate with iron or its oxides, alongside multi-layer adsorption films stabilized by intermolecular hydrogen bonding and Van der Waals forces. These insights will be instrumental in the development of more efficient and effective lubrication materials to meet the demands of modern technology.

A kind of N-containing borate ester (DEBE) with a double five-member-ring structure as a lubricant additive was synthesized by using boric acid, diethanolamine and alkylphenol polyoxyethylene ether as the starting materials.