Extremely Long Chains of Magnetic Particles via Large Plastic Beads Observed in Bimodal Magnetic Elastomers

Abstract

The relationship between the magnetorheology of bimodal magnetic elastomers with high concentrations (60 vol %) of plastic beads with diameters of 8 or 200 μm and the meso-structure of the particles was investigated. Dynamic viscoelasticity measurements revealed that the change in storage modulus of the bimodal elastomer with 200 μm beads was 2.8 × 10 5 Pa at a magnetic field of 370 mT. The change in the storage modulus for monomodal elastomer without beads was 4.9 × 10 4 Pa. The bimodal elastomer with 8 μm beads hardly responded to the magnetic field. In-situ observation for the particle morphology was performed using synchrotron X-ray CT. For the bimodal elastomer with 200 μm beads, a highly aligned structure of magnetic particles was observed in the gaps between the beads when the magnetic field was applied. On the other hand, for the bimodal elastomer with 8 μm beads, no chain structure of magnetic particles was observed. The orientation angle between the long axis of the aggregation of magnetic particles and the magnetic field direction was determined by an image analysis in three dimensions. The orientation angle varied from 56°to 11°for the bimodal elastomer with 200 μm beads and from 64°to 49°for that with 8 μm beads by applying the magnetic field. The orientation angle of the monomodal elastomer without beads changed from 63°to 21°. It was found that the addition of beads with a diameter of 200 μm linked the chains of magnetic particles, while beads with a diameter of 8 μm prevented the chain formation of the magnetic particles.

Particle mobility and macroscopic magnetorheological effects for polyurethane magnetic elastomers

“…Carbonyl iron (CI) with a median diameter of 7.0 μm and with a density of 7.57 g cm −3 (CS Grade BASF SE) was used for magnetic particles. 19,33 The saturation magnetization of CI particles was 210 emu g −1 measured using a SQUID magnetometer (MPMS, Quantum Design Inc.).…”

“…The molar ratio of –NCO to –OH group was constant at 1.00 ([NCO]/[OH]), which is the same as those we previously reported. 17–19 The weight concentration of CI particles was kept at 70 wt%, which corresponds to a volume fraction of 0.23. The PPGs, plasticizer, and magnetic particles were mixed using a hybrid mixer (KK-250S Kurabo, rotation: 3, revolution: 7) for several minutes.…”

“…17,18 We have also demonstrated that the gaps created by the plastic beads in the magnetic elastomer ensure the mobility of the magnetic particles and the MR effect. 19…”

Voids induce wide-range modulation of elasticity for magnetic elastomers II

“…12 We have performed Xray-CT imaging of magnetic elastomers using synchrotron radiation and observed the migration process of magnetic particles in a cross-linked polymer matrix in detail. 13,14 Upon application of a magnetic field, the magnetic particles move simultaneously, overcoming the resistance force from the surrounding polymer matrix, and form short chains. These short chains then connect three-dimensionally around 150 mT and develop into giant clusters with anisotropic shapes.…”