Efficient Chain Formation of Magnetic Particles in Elastomers with Limited Space

Abstract

The magnetic response of the storage modulus for bimodal magnetic elastomers containing magnetic particles with a diameter of 7.0 μm and plastic beads with a diameter of 200 μm were investigated by varying the volume fraction of plastic beads up to 0.60 while keeping the volume fraction of the magnetic particles at 0.10. The storage modulus at 0 mT for monomodal magnetic elastomers was 1.4 × 104 Pa, and it slightly increased with the volume fraction of plastic beads up to 0.6. The storage modulus at 500 mT for bimodal magnetic elastomers at volume fractions below 0.25 was constant, which was equal to that for the monomodal one (=7.9 × 104 Pa). At volume fractions of 0.25–0.40, the storage modulus significantly increased with the volume fraction, showing a percolation behavior. At volume fractions of 0.40-0.60, the storage modulus was constant at 2.0 × 105 Pa, independently of the volume fraction. These results indicate that the enhanced increase in the storage modulus was caused by the chain formation of the magnetic particles in vacancies made of plastic beads.

Magnetically Tunable Transmissibility for Magneto-Responsive Elastomers Consisting of Magnetic and Nonmagnetic Particles

“…Therefore, the magnetization of ZnO should not affect the remarkable changes in modulus for bimodal elastomers because the magnetization of CI particles was far larger than that of ZnO (70.7 emu/g at 82 mT). The large increase in the storage modulus for the bimodal elastomer is due to the chaining of magnetic particles via nonmagnetic particles as we have presented previously. − Since the nonmagnetic particles are immobile even applying magnetic fields, the probability of physical contact between magnetic particles and nonmagnetic particles while making the chain structure . The relative changes in storage modulus for monomodal and bimodal elastomers were 10.2 and 5.1 folds at 80 mT, respectively, which are not much larger than those investigated in our previous studies.…”

“…A bimodal elastomer consists of magnetic particles and nonmagnetic particles. Large changes in storage modulus are obtained by intervening the chain structure of magnetic particles with that of nonmagnetic particles. − High loading of both magnetic and nonmagnetic particles increases the number of contacts among particles, resulting in a significant MR effect. Also, bimodal elastomers demonstrate fast response to elasticity changes when a magnetic field is applied .…”

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

“…Tolylene diisocyanate (Fujifilm Wako Chemicals, Ltd.) was used as a linker, and bis­(2-ethylhexyl) phthalate (Fujifilm Wako Chemicals, Ltd.) was used as a plasticizer. The molar ratio of −NCO to the −OH group was constant to be 1.00 (= [NCO]/[OH]), which is the same as those we previously reported. ,,, The prepolymer, PPGs, plasticizer, magnetic particles, and plastic beads were mixed by a spatula for several minutes. The mixed liquid was filled into a silicon mold and cured for 30 min at 100 °C.…”

“…We have studied thus far methodologies for enhancing the MR effect. − In those studies, we investigated the MR effect of polyurethane magnetic elastomers and found that bimodal magnetic elastomers with magnetic and nonmagnetic particles exhibit a significant MR effect compared to monomodal magnetic elastomers. − In previous studies, zinc oxide with a diameter of 10.6 μm and aluminum hydroxide with a diameter of 1.4 μm were used as nonmagnetic particles. , When a magnetic field of 500 mT is applied to a bimodal magnetic elastomer with 12 vol % zinc oxide particles, the increase in storage modulus is 500 kPa, which is 4.2 times that of the monomodal (120 kPa) . The increase in the storage modulus of a bimodal magnetic elastomer with 6.6 vol % aluminum hydroxide particles is 3.27 MPa, which is 4.3 times that of the monomodal (754 kPa) .…”

“…The increase in the storage modulus of a bimodal magnetic elastomer with 6.6 vol % aluminum hydroxide particles is 3.27 MPa, which is 4.3 times that of the monomodal (754 kPa) . The change in storage modulus of a magnetic elastomer with 200 μm plastic beads (PMMA) is 260 kPa, which is 5.8 times that of monomodal (45 kPa) . It is considered that this is due to the efficient chaining of magnetic particles in the gaps created by the beads filled with a body-centered cubic structure, which improves the magnetorheology.…”