Ball milling-assisted preparation of polyether-functionalized covalent organic frameworks with controlled morphology for high-efficiency oil lubrication

In this work, a functionalized fluorinated covalent organic framework (COF-F) is successfully fabricated via a two-step strategy involving solvothermal synthesis followed by surface modification. First, the aldehyde-terminated COF-F was fabricated via a solvothermal method. Subsequently, amino terminated polyether (ATPE) was grafted onto COF-F by ball milling through the Schiff base reaction of the aldehyde groups of COF-F with the amine groups of ATPE, thereby obtaining ATPE-functionalized COF-F (ATPE@COF-F). Tribological experiments showed that the addition of 2.00 wt% ATPE@COF-F into the base oil PAO10 markedly improves its lubricating properties, decreasing the wear volume from 1.0 × 10⁶–8.5 × 10⁴ µm³ and reducing the average friction coefficient from 0.231 to 0.106. This remarkable improvement primarily is the result of the synergistic polishing, mending, and rolling effects of ATPE@COF-F, as well as the generation of a tribochemical protective film, which separates the contacting surfaces and prevents direct asperity contact. Moreover, ATPE@COF-F samples with different morphologies were prepared by varying the solvent ratio. While the friction coefficient of ATPE@COF-F show minimal variation across morphologies, their wear volume differ markedly, with the spherical morphology delivering the optimal anti-wear performance.