Manipulating the structure of covalent organic frameworks through ball-milling preparation toward excellent tribological properties in PEG base oil

This study investigated the tribological performance and lubrication mechanism of two distinct covalent organic frameworks (COFs), two-dimensional aromatic polyamides (2DAPA) with either a normal level of crystallinity (2DAPA-15 min) or a high level of crystallinity (2DAPA-240 min). Friction tests showed that 1.00 wt.-% 2DAPA-240 min enhanced PEG400's anti-wear properties with a 29.10 wt.-% wear volume reduction and stable friction coefficient (∼0.05), outperforming 2DAPA-15 min. The wear surface exhibits minimal adhesive/abrasive damage, attributed to flake-like 2DAPA exfoliation under friction, forming a physical protective barrier via uniform deposition. The chemical adsorption of -NH₂ groups onto metal surfaces and Cl-driven FeCl₃ reaction films, alongside tribo-oxidation products (Fe₃O₄, Cr₂O₃) and carbon-based (C-C/C-O/C-N) deposits that strengthen film stability. Notably, 2DAPA improves the tribological properties of PEG400 through the synergistic effect of physical deposition and chemical film formation. The findings of this study provide a solid theoretical basis for the development of high-performance lubricants based on 2D materials, paving the way for their practical application in various industries.