Macroscale superlubricity under ultrahigh contact pressure in the presence of layered double hydroxide nanosheets

It is difficult to achieve macroscale superlubricity under high contact pressures and high normal loads. Layered double hydroxide (LDH) nanoadditives were introduced into an ionic liquid alcohol solution (IL(as)) with contact pressures up to 1.044 GPa, which resulted in a friction coefficient (COF) of 0.004 and a robust superlubricity state lasting for 2 h. Compared with the LDH particles (LDH-Ps) with ca. 90-nm widths and 18-nm thickness, micron-scale LDH nanosheet (LDH-N) additives with ca. 1.5-µm width and 6-nm thickness increased the load-bearing capacity by approximately three times during superlubricity. The lubricant film thickness and the ultrathin longitudinal dimension of the LDH-N additives did not influence the continuity of the fluid film on the contact surface. These improvements resulted from the protective adsorption layer and ion distribution formed on the contact interface, as revealed by detailed surface analyses and simulation studies. In particular, the sliding energy barrier and Bader charge calculation revealed that weak shear sliding between the nanosheet and the solid surface formed easily and the anions in the liquid adsorbed on the solid surface exhibited electrostatic repulsion forces, which generated stable tribological properties synergistically. This research provides a novel method for obtaining macroscale superlubricity for practical industrial applications.