Solvent-free covalent MXene nanofluid: A new lubricant combining the characteristics of solid and liquid lubricants

A sole liquid lubricant or solid lubricant cannot cater to the demands of high-efficiency lubrication performance. From the standpoint of fusion of solid and liquid lubrication, solvent-free nanofluids are expected to be promising lubricants. In this work, solvent-free covalent MXene nanofluids were synthesized by grafting MXene with organosilane (KH560) and polyether amine oligomer (M2070) via covalent linkage. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetric analysis and rheological characterizations demonstrated that the MXene nanofluids were successfully synthesized and presented macroscopic fluidity at room temperature. Importantly, when used as a lubricant, the nanofluids perform well in friction-reduction and anti-wear properties even at high velocity (50 Hz), elevated temperature (100 degrees C), and heavy load (1100 N). The excellent tribological properties are ascribed to the nanofluids inte-grating the advantages of significantly improved load-bearing capacity and lubrication performance of the core nanomaterials, as well as liquid-like fluidity and self-healing characteristics of the organic shell. Moreover, the formation of 120-180 nm thick tribofilm on the worn steel surface was identified, which is significant in improving the lubrication performance. The above results suggest that the solvent-free MXene nanofluids should be a quite excellent candidate lubricant for integrating the advantages of solid and liquid lubricants and provide theoretical guidance for structural design of high-performance solvent-free nanofluid lubricants.