Oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient friction and wear reduction

Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure, suitable mechanical property, and tunable surface functionalities. However, the poor compatibility between nanomaterials and base oil limits their further applications. In this work, we demonstrated oil-soluble poly (lauryl methacrylate) (PLMA) brushes-grafted metal-organic frameworks nanoparticles (nanoMOFs) as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance. Macroinitiators were synthesized by free-radical polymerization, which was coordinatively grafted onto the surface of the UiO-67 nanoparticles. Then, PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization, which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil. By adding UiO-67@PLMA nanoparticles into the 500 SN base oil, coefficient of friction and wear volume reductions of 45.3% and 75.5% were achieved due to their excellent mechanical properties and oil dispersibility. Moreover, the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives, and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120 °C. Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.