Magnetorheological carbonyl iron particles doubly wrapped with polymer and carbon nanotube

To improve magnetorheological (MR) characteristics of carbonyl iron (CI) microparticles, we introduce two-step CI coating procedures with poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotube (MWNT) for the first time. Core(CI)-shell(PMMA) (CI-PM) structured composite magnetic microbeads were synthesized by dispersion polymerization first, showing improved dispersion stability and sedimentation quality. However, its magnetic strength was decreased compared with that of pristine CI-based MR fluid. To enhance its magnetic strength, the core-shell type CI-PM particles were wrapped with MWNT via ultrasonication. Rheological properties of their MR fluid were measured by a rotational rheometer with a magnetic field supplier. The CI-PMMA-MWNT (CI-PM-NT) particles were found to show better flow and dynamic rheological properties compared to those from CI-PM particles while density of the CI-PM-NT particles was not much different from that of CI-PM, implying that sedimentation stability of the CI-PM-NT particles was also being kept. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3058674]