Superlubricity Modulation by Molecular Structure of Two-Dimensional Zeolite Imidazole Frameworks

Zeolite imidazole frameworks (ZIFs) have the advantages of high surface stiffness of inorganic materials and low surface free energy of organic materials, which is expected to be an ideal material to achieve solid superlubricity. In this paper, based on the evolution law of the adhesion and surface stiffness of ZIF@mIm and its complexes with structural parameters, superlubricity was obtained on ZIF@mIm + eIm surface (friction coefficient as low as 0.0076), and the influence mechanism of adhesion and surface stiffness on the lubrication properties was revealed. Firstly, the adhesion work between ZIFs and probe is positively correlated with the surface free energy of ZIFs, and the essence is that its ligand affects the anchoring effect strength between metal atom and the tip. Secondly, increasing Zn–N coordination bond strength improves surface stiffness, thereby reducing the out-of-plane deformation. By adjusting the molecular structure, the friction energy dissipation will be reduced from the above two aspects, so as to achieve superlubricity modulation. This is helpful to establish the structure-function relationship between structural parameters and lubrication performance, promising for the precise design of two-dimensional superlubricity materials.