Polymer Coated Smart Magnetic Microspheres and Their Magnetorheology

초록

Magnetorheological (MR) fluids as intelligent and smart materials with a large and tunable increase in rheological characteristics such as shear viscosity and yield stress under an external magnetic field have drawn a huge attention. When the magnetic field is imposed, its viscoelastic properties vary by showing a characteristic fibrillation, with strings of the particles oriented along the magnetic field direction. Carbonyl iron (CI) particles are known to be superior candidate of MR fluids due to their high saturation magnetization and appropriate particle size, however, they have severe sedimentation problem due to the large mismatch of the particle density to the carrier oil. Therefore, our efforts on improving MR characteristics of the magnetic particles along with their rheological analysis will be focused. Coating the surface of CI particles produces favourable core-shell structure along with apparently decreased density for synthesized composite particles with various polymers via either solvent casting or conventional in-situ dispersion polymerization. Double wrapping process with polymeric shells and MWNT layers were also studied. MR characterizations are investigated via rotational and oscillation mode tests. Yield stress and flow curve are examined based on model equations. MR elastomers based on modified CI particles will be also covered.