Effects Of Surface Modified Fe₃O₄ Nanoparticles On The Rheological Properties Of Bidisperse Magnetorheological Fluids

Magnetorheological (MR) fluid is a prospective smart fluid, which rheological characteristics would change upon the application of a magnetic field. Therefore, it can be used in all kinds of adaptive structure systems, such as adaptive structures for aerospace systems, civil engineeringand vehicles. And the anti-vibration capability of these systems could be significantly improved. Magnetorheological (MR) fluids are typically made by suspending spherical micron-sized magnetic particles (e.g. iron microspheres) in a carrier fluid such as silicone oil or water. Unfortunately, magnetic particles in MR fluids are prone to sedimentation in the absence of constant or frequent mixing because of density difference between magnetic particles and carrier liquids, and the sediment particles would further agglomerate, resulting in undesired, tightly bound particle clusters, which would make re-dispersion very difficult, even finally rendering the MR fluids ineffective. In this work, we try to develop a method to improve the stability and maintain the yield stress of MRFs through investigating the characteristic properties of bidisperse magnetorheological fluids. The processes are as follows:at first, synthesize a surface hydrophobic surface modification of Fe3O4 nanoparticles, and then prepare bidisperse magnetorheological fluids with carbonyl iron particles and the modified Fe3O4 nanoparticles with different mass ratio; thirdly, investigate the change rules of the stability, yield stress and off-state viscosity of the MR fluids, through comparing with those of the similar bidisperse magnetorheological fluids with carbonyl iron particles and pure Fe3O4 nanoparticles.The results of XRD, SEM, FT-IR, VSM, size distribution, and contact angle testing demonstrate that the synthesized modified Fe3O4 nanoparticles were shown to be crystalline state, and superparamagnetic and hydrophobic, and the particle size distribution mainly is between 20nm and 50nm.The stabilities and rheological properties of the synthesized bidisperse magnetorheological fluids were experimentally investigated. The test results show that the stabilities of bidisperse magnetorheological fluids with modified Fe3O4 nanoparticles is much better than that of the traditional MRFs, the yield stress of bidisperse magnetorheological fluids had also been improved. And there is an optimal ratio, i.e., when the modified Fe3O4 nanoparticles is 1.5%, both of the stability and yield stress of MRFs are optimal, the stability of settlement increased by 25%, and yield stress increased by nearly 26.5%.