Synthesis of core-shell formed carbonyl iron/polydiphenylamine particles and their rheological response under applied magnetic fields

Soft-magnetic carbonyl iron (CI) microspheres were coated with conducting polydiphenylamine (PDPA) using an oxidative dispersion polymerization process to produce core-shell-structured CI/PDPA particles for magnetorheological (MR) applications. The CI particles were initially modified with a p-amino benzoic acid to enhance their affinity to PDPA. The surface morphology of the CI/PDPA core-shell particles was characterized by scanning electron microscopy. The chemical composition, weight and atom percentage, thermal properties, and magnetism of the composites were investigated by X-ray energy dispersive spectroscopy, Fourier-transformed infrared spectroscopy, thermogravimetric analysis, and vibrating-sample magnetometry, respectively. The rheological behavior of the MR fluids for both pristine CI and CI-PDPA particles dispersed in silicone oil was measured using a rotating rheometer. The sedimentation characteristics of the CI/PDPA-based MR fluid with improved dispersion stability due to the reduced density mismatch was analyzed further using a Turbiscan.