Effect Of Surface Graft Modification On Tribological Behaviors Of Nanodiamonds

Friction and wear are the main modes of energy dissipation and components failure in moving mechanical assemblies.Therefore,it is very necessary to explore the lubrication mechanism.Lubricants are divided into lubricating oil,lubricating grease,water-based lubricant and solid lubricant.Among them water-based lubricant is considered to be valuable due to its excellent cooling performance,low price and particularly low pollution.In this study,inspired by mussels which can be firmly attached to rocks and the ultra-low lubrication of articular cartilage,dopamine similar to mussel foot silk and 2-methacryloyloxyethylphosphocholine(MPC)similar in structure to articular cartilage were selected as the main material.Grafting to and grafting from are used to modify the surface of nanodiamonds(ND).Characterization of nuclear magnetic resonance H and C spectra,transmission electron microscopy,X-ray photoelectron spectroscopy,Fourier transform infrared spectroscopy and thermogravimetric analysis indicated that DMA-MPC was successfully modified onto the ND surface.Tribological experiments show that:(1)In this study,the surface modification modification of ND was first carried out by grafting to method.The zwitterionic copolymer DMA-MPC was first synthesized and then entirely coated onto the ND surface.The addition of nanoparticles to the lubricant can significantly reduce wear on the grinding balls and on the grinding disc.This can be attributed to the rolling effect of the nanoparticles.The friction coefficient of the modified nano-diamond powder was significantly reduced(The COF was reduced from 0.028 to 0.017,which was reduced by about 40%).This can be attributed to the hydration lubrication of the zwitterionic brush on the ND surface.(2)Secondly,the grafting from method was used to prepare long-chain MPC molecular brushes by using the active groups from ND and two-stage reaction platform by coating dopamine.Among them,the method by using the active groups from ND is insufficient to provide a graft site of sufficient density,because the number and density of the surface groups of the ND are insufficient,so the result was contrary to the target.By coating dopamine to provide a secondary reaction platform,the laws and trends of the friction data are consistent with the results of the grafting to method.The COF was much lower than the grafting to method(The COF was reduced from 0.028 to 0.015,which was reduced by about 46%).The above results show that the MPC molecular brush requires a certain density to have a hydration lubrication effect,and the longer the molecular brush length,the better the hydration lubrication effect.