Particle mobility and macroscopic magnetorheological effects for polyurethane magnetic elastomers

The relationship between the particle mobility and magnetorheological effect was investigated for polyurethane magnetic elastomers containing carbonyl iron particles with various cross-linking densities or plasticizer concentrations. The storage modulus at 0 mT increased and the on-field modulus at 500 mT decreased with the cross-linking density. The critical magnetic field where the storage modulus starts to rise up increased with the cross-linking density, indicating that the movement of magnetic particles is depressed by the cross-linking points of the polyurethane network. Magnetic elastomers with various plasticizer concentrations revealed that the storage modulus at 0 mT decreased and the on-field modulus at 500 mT increased with the plasticizer concentration. The critical magnetic field decreased with increasing plasticizer concentration, indicating that a dense polyurethane network prevents magnetic particles from moving. It was found that the change in the modulus due to the magnetic field can be scaled by the storage modulus at 0 mT as well as the critical magnetic field. Thus, there is a certain correlation between the macroscopic modulus of elasticity (storage modulus at 0 mT) and the microscopic mobility of magnetic particles reflected in the critical magnetic field. The critical magnetic field of magnetic elastomers was proportional to the storage modulus at 0 mT, suggesting that the force required to move the magnetic particles increases proportionally to the storage modulus at 0 mT.