Preparation and rheological properties of highly stable bidisperse magnetorheological fluids

The utilization of magnetic nanofluids as the base carrier liquid proves to be an effective strategy for enhancing the stability of magnetorheological fluids. However, the preparation method for bidispersed magnetorheological fluids still deserves further investigation. In this study, Fe3O4 nanoparticles were synthesized through chemical co-precipitation, and aviation hydraulic oil-based magnetic nanofluids were prepared using myristic acid as a surfactant. Micron-sized particles, modified with the same surfactant, were dispersed into the magnetic nanofluids, resulting in a novel bidisperse magnetorheological fluid (C-MRFF). The coated particles underwent physical phase analysis and magnetic property testing through an x-ray diffractometer, Fourier infrared spectrometer, transmission electron microscope, scanning electron microscope, and vibrating sample magnetometer. Due to the addition of nanoparticles, C-MRFFs exhibited superior stability to micron-sized particle-based magnetorheological fluids. They demonstrated the best sedimentation stability and redispersibility at a 9% mass fraction of nanoparticles. Thanks to the protection of the micron-sized particle surface coating, C-MRFFs displayed superior sedimentation stability to traditional bidisperse magnetorheological fluids over a wide temperature range. The magnetorheological properties of C-MRFFs were studied. The results indicated that the yield stress of C-MRFFs increased with increasing magnetic field strength or decreasing temperature. The increase in the mass fraction of nanoparticles was beneficial to the increase in yield stress until severe settling of C-MRFFs occurred. In comparison to micron-sized particle-based magnetorheological fluids, C-MRFFs exhibited higher yield stresses. Although the yield stress of C-MRFFs was slightly lower than that of traditional bidisperse magnetorheological fluids due to the surface coating of larger particles, they exhibited stronger shear resistance over a wide temperature range.