Self-assembled bio-inspired cauliflower-like MnFe₂O₄ nanospheres as dispersed materials for high-stability magnetorheological fluid

In this research, novel hierarchically structured cauliflower-shaped MnFe₂O₄ nanospheres were synthesized via a simple solvothermal method and their potential application for high performance magnetorheological fluids was investigated. The samples were comprehensively characterized using FE-SEM, TEM, FTIR, XRD, BET, TGA, XPS and VSM. It was revealed that the prepared MnFe₂O₄ nanospheres exhibited hierarchical cauliflower-like morphology and the average particle size was found to be 182 nm. More importantly, the MnFe₂O₄ nanospheres demonstrated typical mesoporous structure, high specific surface area of 30.3 m²/g and moderate saturation magnetization of 29.3 emu/g, which were suitable for preparation of a uniform and stable MR suspension. The rheological performances comprising shear stress, viscosity, storage modulus and loss modulus of MR fluid under different external magnetic fields were measured using a dynamic rotational rheometer. The results indicated that the MR fluid possessed enhanced MR responses as the magnetic field intensity increased, which were attributed to the rapid formation of robust chain-like structures composed of MnFe₂O₄ nanospheres inside the MR suspension. In addition, it was observed that the sedimentation stability of MR fluid containing MnFe₂O₄ nanospheres was much more prominent than that of the suspension based on spherical carbonyl iron particles in the same testing period.