Rheological and Tribological Properties of Ionic Liquid-Based Nanofluids Containing Functionalized Multi-Walled Carbon Nanotubes

Room temperature ionic liquid-based nanofluids containing functionalized multi-walled carbon nanotubes (F-MWCNTs) were fabricated. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectra revealed the morphology and chemical structure of the obtained F-MWCNTs. The rheological behaviors of the F-MWCNTs/1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF 6 ]) nanofluids were studied, demonstrating the shear thinning behavior of nanofluids at rather low concentrations, which could be due to the high specific ratio, flexibility of F-MWCNTs, and the formation of a transient network through nanotube−nanotube and nanotube−matrix interactions. It was found that the rheological behavior of the F-MWCNTs (0.1 wt %)/[Bmim][PF 6 ] nanofluid was similar to that of the surfactant worm-like micelle systems. Therefore, the transient network structure of the F-MWCNTs (0.1 wt %)/[Bmim][PF 6 ] nanofluid could be renovated in a short time after shearing forces were input. The shear viscosity of the nanofluids was even lower than that of pure [Bmim][PF 6 ], especially under high shear rates, which could be attributed to the self-lubrication of F-MWCNTs. The tribological properties of the nanofluids were also evaluated in comparison with those of pure [Bmim][PF 6 ] under loads in the range of 200−800 N, indicating that the nanofluids exhibited preferable friction-reduction properties under 800 N and remarkable antiwear properties with use of reasonable concentrations.