Smart polymer self-lubricating material: Optimal structure of porous polyimide with base oils for super-low friction and wear

Abstract

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.