In the contemporary pursuit of ensuring long-term lubrication for transmission units operating under harsh conditions, significant challenges remain. Researchers have investigated porous polymer materials as potential solutions; however, achieving exceptionally low friction and wear has proven elusive. To address this issue, we developed a novel porous fluorinated polyimide (PPIF-250) characterized by superior mechanical performance, heat resistance, and higher oil content and retention than other porous polyimide (PPI) with comparable pore sizes and porosities. Extensive lubrication testing under varying conditions has demonstrated that PPIF-250 achieves remarkably low friction and wear characteristics, even under high FV (force × velocity) 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 polyethylene glycol 200 (PEG200) with a tailored PEG-200 structure results in significantly improved oil content, retention, and long-term lubrication relative to those of 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 multilayer 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.

Inorganic nanoparticles have been proved as powerful lubricant additives at elevated temperature. However, the tribological properties are inevitably impaired due to poor dispersion and insufficient high temperature resistance of organic matter modified nanoparticles. Here, we prepare a self-dispersed molybdenum disulfide quantum dot/graphene crumpled ball (MGCB) comprising molybdenum disulfide quantum dot uniformly interspersed on the wrinkled graphene ball. The crumpled ball composite possesses excellent dispersity in polyalkylene glycol base oil without depending on surface modifiers. Compared with the conventional phosphate esters lubricant, our results indicate MGCB could vastly improve the lubrication performance of polyalkylene glycol with an extremely low concentration (0.05 wt%) at elevated temperature (150 °C), showing a friction reduction of 47% and a wear reduction of 30% compared with the conventional phosphate esters lubricant (tricresyl phosphate, TCP). This is because crumpled ball potentiates synergistic lubrication effect within the boundary lubrication. Overall, we envision our designed self-dispersed MGCB has significant potential in tribological application at elevated temperature.

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.