MOF-structure-dependent mechanical and tribological properties of polyimide composite coatings: synergistic experimental and computational insights

Due to their unique organic–inorganic hybrid structures, metal–organic frameworks (MOFs) have shown increasing potential as fillers for polymer self-lubricating composites. In this study, a systematic investigation of three structurally different MOFs (ZIF-8, MOF-5, and UiO-66, each at 3 wt%) in polyimide (PI) composite coatings revealed that their incorporation enhanced the mechanical properties. Notably, UiO-66 exhibited the most pronounced reinforcement, attributable to its strong interfacial bonding with the resin matrix, which led to an 18.4% increase in tensile strength as well as corresponding enhancements in elastic modulus and hardness. To gain insight into the friction and wear mechanisms of MOFs/PI composite coatings, ball-on-disc tests were complemented by molecular dynamics (MD) simulations and density functional theory (DFT) calculations. This combined approach elucidated the role of MOFs at the frictional contact interface and their influence on transfer film formation. The conclusions regarding the intrinsic relationship between the structure of MOFs and their tribological mechanisms are of both theoretical and practical importance for developing PI composite coatings for self-lubricating bushings, bearing shells and sliders.