The relationship between surface structure and super-lubrication performance based on 2D MOFs

Metal-Organic Frameworks (MOFs) have the potential to be super-lubricative materials because their advantages of inorganic-organic hybridization and molecular-level regulation. MOFs constructed from Cu2+ and meso-Tetra(4-carboxyphenyl)porphine (TCPP) can act as an excellent candidate in previous predictions. In this work, the CuTCPP with various surface structure were designed to investigate the specific influence of surface microstructure on the micro-friction performance. The experimental results showed that the lubrication performance is determined by the surface structure. When the surface is changed from the undefiled state to the modified state with surfactants, the friction coefficient quadrupled (5.6*10−4 to 2.1*10−3) and the adhesion doubled (4.4 to 8.7 nN). We innovatively observed the surface structure through the atomic friction maps and figured out their influencing mechanisms on the friction performance. The anchoring effect is the main source of friction on the undefiled CuTCPP surface, while the entanglement, viscous hysteresis or persistent viscous state become the dominant factor for the CuTCPP surface decorated with SDS, CTAB or PVP molecules respectively. In addition, the positive effect of surface porosity on friction reduction was confirmed. Therefore, the relationship between the tribological properties and the surface structure was successfully established that can guide the future research on super-lubricative materials.