Fabrication of Polyindole-Coated Zinc Ferrite Particles and Their Dual Rheological Response Under Magnetic and Electric Fields

ZnF ₂ O ₄ /polyindole (PIn) core/shell particles were synthesized using a solvothermal method followed by an oxidative polymerization process. The synthesis was relatively simple, and the ZnFe ₂ O ₄ core was found to have suitable magnetic properties as a magnetorheological (MR) particle. The ZnFe ₂ O ₄ /PIn particles had a uniform and spherical morphology with their saturation magnetization of 42.59 emu/g. Field emission transmission electron microscopy was used for characterization. The ZnF ₂ O ₄ /PIn particles were suspended in silicone oil at 5 vol.% for electrorheological/MR (E/MR) fluid preparation. Steady shear and dynamic tests were performed under each magnetic and electric field by a rotational rheometer to analyze the dual-responsive rheological properties of the ZnF ₂ O ₄ /PIn-based E/MR fluid. Under a magnetic field, the power-law exponents of both dynamic and elastic yield stresses were observed to be 1.0, while their ER response was observed directly from optical microscope.