A molecular dynamics study on the lubrication performance of ionic liquids

HD Jiang and YF Yu and WW Tang and RH Zhou and WJ Shi and LC Bai, JOURNAL OF MATERIALS SCIENCE, 57, 18874-18888 (2022).

DOI: 10.1007/s10853-022-07744-1

The influence of ionic liquids (ILs) on the friction of diamond-like carbon (DLC) films is investigated via molecular dynamics simulation. The effects of load, amount of ILs molecules, roughness and sliding velocity are considered. It is found that a large amount of ILs films can prevent the formation of C-C bonds between sliding interfaces. The friction in this case increases with loads, due to a closer arrangement of ILs and high cohesive energy between ILs and DLC films. Moreover, for the cases with a small amount of ILs under a large load, the ILs molecules are locally distributed, inducing the transition of the lubrication state from fluid lubrication into boundary lubrication, which promotes the interfacial C-C bonds formation and accounts for large friction. Furthermore, the integrity of ILs films is broken by high sliding velocity, but the friction is almost unchanged. This is because the graphitization level of DLC films increased by the high velocity can eliminate the friction enhancement by the bond formation between these films. Fast Fourier transform (FFT) analyses show that the frequency of friction oscillations generally agrees well with that of the velocity of center of mass, demonstrating that the intrinsic diffusion properties of ILs determine the friction mechanisms.

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