Fabrication and magnetic stimuli-response of polydopamine-coated core-shell structured carbonyl iron microspheres

Soft magnetic carbonyl iron (CI) for application to magnetic stimuli-responsive smart materials in an external magnetic field normally implies severe sedimentation problems because of the density imbalance between the CI particles and the dispersed medium. As a new method of ameliorating this problem, CI/polydopamine (PDA) composite particles with core-shell structure were synthesized via an oxidative self-polymerization process, bringing into an account of the coating efficiency of the PDA. Surface morphology of the CI/PDA composite particles was characterized by scanning electron microscopy, while Fourier transform infrared spectroscopy, X-ray energy-dispersive spectroscopy, and vibrating sample magnetometry were adopted to measure the chemical composition, weight and atomic percentages, and magnetic properties of the fabricated composites. The magnetic stimuli-response of their magnetorheological (MR) properties was examined by using a rotational rheometer at various magnetic field strengths and compared with pristine CI-particle-based MR fluid. The measured dynamic yield stress was fitted to a universal yield stress equation well. The sedimentation properties of the CI/PDA-composite-based MR fluid were further examined by a Turbiscan (TM). In addition, the anti-corrosion characteristic of these particles was also investigated.