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

[Display omitted] •Hierarchical structured MnFe2O4 nanospheres were prepared through a solvothermal method.•Uniform particle size, mesoporous characteristic and superparamagnetic behavior.•A high performance magnetorheological fluid based on MnFe2O4 nanospheres.•Typical magnetorheological effect and improved sedimentation stability were achieved. 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.