Two-layer coating with polymer and carbon nanotube on magnetic carbonyl iron particle and its magnetorheology

Magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids generally posses serious dispersion defects due to the large density mismatch between the CI particles and continuous oil medium, which restricts further MR applications. Polymer coating technology has been introduced in an attempt to reduce the density or prevent CI particle aggregation. In this study, a unique functional coating composed of a polyaniline layer and multiwalled carbon nanotube nest was fabricated on the surface of CI particles using a dispersion polymerization and solvent casting method to improve the sedimentation problem of CI-based MR fluids when dispersed in medium oil. The coating morphology was analyzed by scanning electron microscopy. The effect of the functional coating on the MR performance along with the sedimentation observations was investigated using a rotational rheometer. The results showed that the sedimentation of dispersed particles was improved considerably by the reduced density and rough morphology.