ИСТИНА

Magnetorheological elastomer (MRE) is a polymer matrix filled with micron or nanosize magnetic particles. Such elastomers are the example of smart materials – a new class of materials those properties could be reversibly controlled by the external magnetic field. Particularly, MRE is able to significantly change its rheological characteristics in presence of homogeneous magnetic field of rather small density (0-1000 mT). In this work several different MREs were investigated. Elastomers are based on silicone rubber matrix. 2 types of MREs were synthesized. The first type of elastomers is filled with soft magnetic particles: carbonyl iron (CI), 3-50 microns in diameter. Samples have different modulus of matrix (soft and hard matrices were used), different weight percentage of filler (0 %, 70 %, 82 %) and different spatial distribution of particles (isotropic and anisotropic). The second type of elastomers is filled with hard magnetic particles: FeNdB 10-70 microns in diameter. Samples have different spatial distribution of particles (isotropic and anisotropic). After curing, all samples were magnetized in homogeneous magnetic field of different intensity (0, 3, 6, 9, 12, 15 kOe). All rheological measurements were made using the commercial rheometer Anton Paar, model Physica MCR 301, with measuring “plate-plate” unit and a magnetic cell. Mechanical properties of the material were investigated in different measuring modes. The first step was the frequency and the amplitude tests of dynamic modulus in the absence and presence of magnetic field B. Dependencies of the storage modulus G'(f, B) and the loss modulus G''(f, B) on the oscillation frequency f at constant strain amplitude as well as dependencies G'(γ, B), G''(γ, B) on the strain amplitude at constant frequency were obtained. The second step was the investigation of time behavior of the moduli G'(t, B), G''(t, B) and the normal force FN(t, B) at fixed strain amplitude and oscillation frequency. One can say that in magnetic field a huge increase of the moduli was observed. In the magnetic field of 0.6 T the storage modulus increases in 2-3 orders, loss modulus – in 1-2 orders. When the specimen is placed in a constant homogeneous magnetic field the storage modulus increases and has a tendency to saturate. However, samples have relaxation time that depends on the shear strain and system does not reach the equilibrium state for a long time. Normal force significantly increases in the presence of magnetic field as well. This phenomenon could be explained by the process of structuring of magnetic particles within the matrix. Particles form chains aligned to the direction of magnetic field and these chains form some kind of a net structure that makes sample stiffer. Financial support of the Russian Foundation for Basic Research and the International Bureau of the BMBF (grant Nr. 01DJ13006) is gratefully acknowledged.