Supramolecular composite gel lubricants with polymer brush-grafted MOF additives for enhanced friction and wear reduction

Supramolecular gels hold great potential in engineering applications as lubricants. However, the pure organic network of the gel limits its rheological and lubrication performance. Here, we report a nanoporous material-functionalized supramolecular composite gel lubricant by incorporating polymer brush-grafted metal-organic framework (MOF) nanoparticles (NPs) as nanoadditives. The composite gel was produced by encapsulating poly(lauryl methacrylate) (PLMA) polymer brush-functionalized UiO-67 (UiO-67@PLMA) NPs in 500 SN base oil of a three-dimensional (3D) network formed by 12-hydroxystearic acid (12-HSA) through hydrogen bonding and van der Waals (vdW) interactions. The addition of UiO-67@PLMA NPs largely improved the thermal and rheological properties of the 12-HSA/500 SN gel, and the storage modulus and loss modulus increased significantly. Tribological tests showed that incorporating 0.40 wt% UiO-67@PLMA NPs into the composite gel reduced the coefficient of friction and wear volume by 45.68% and 86.85%, respectively. Furthermore, the UiO-67@PLMA gel demonstrated remarkable tribological performance under challenging conditions, such as 400 N, 65 Hz, and 160 °C. The outstanding lubrication performance of the supramolecular composite gel arises from the shear-triggered release of base oil and nanoadditives, which act as nanobearings and promote protective film formation.