Electric and magnetic field-responsive suspension rheology of core/shell-shaped iron oxide/polyindole microspheres

In this study, conductive polyindole (PIn) was coated onto initially fabricated magnetic iron oxide (Fe₃O₄) particles via chemical oxidative polymerization, and the synthesized core–shell structured hybrid smart particles were used as smart electrorheological/magnetorheological (EMR) materials. The synthesized Fe₃O₄/PIn particles were characterized using scanning electron microscopy and transmission electron microscopy. In addition, the chemical composition of the synthesized particles was confirmed using Fourier-transform infrared spectroscopy. Their magnetic properties were further analyzed using VSM. Consequently, the Fe₃O₄/PIn particle-based suspension, which was both magnetic and conductive, was found to exhibit interesting dual stimuli under both external electric and magnetic fields. Various rheological measurements, including shear simple steady shear and dynamic tests, were employed to evaluate the behavior of typical EMR suspensions. Furthermore, the dielectric properties of the particles were analyzed using an LCR meter. Based on the dielectric spectrum data, the relaxation time (λ) was estimated to be 1.5 × 10^–8 s at the maximum frequency (λ = 1/2πfmax). Measurements conducted using a Turbiscan indicated enhanced sedimentation stability of the particles owing to a decrease in the particle density from 4.34 to 2.93 g/cm³.