The magnetorheological response for magnetic elastomers containing carbonyl iron (CI) particles with a diameter of 6.7 μm coated with poly(methyl methacrylate) (PMMA) was investigated to estimate the diameter of secondary particles from the amplitude of magnetorheological response. Fourier-transformed infrared spectroscopy revealed that the CI particles were coated with PMMA, and the thickness of the PMMA layer was determined to be 71 nm by density measurement. The change in the storage modulus for magnetic elastomers decreased by coating and it was scaled by the number density of CI particles as ΔG~N2.8. The diameter of secondary particle of CI particles coated with PMMA was calculated to be 8.4 μm. SEM images revealed that the CI particles coated with PMMA aggregated in the polyurethane matrix.
Keywords: magnetic elastomer; soft material; stimuli-responsive gel.