No abstract

Ferroelastic composites are smart materials with unique properties including large magnetodeformational effects, strong field enhancement of the elastic modulus and magnetic shape memory. On the basis of mechanical tests, direct microscopy observations and magnetic measurements we conclude that all these effects are caused by reversible motion of the magnetic particles inside the polymeric matrix in response to an applied field. The basic points of a model accounting for particle structuring in a magnetoactive elastomer under an external field are presented.

The new generation of magnetic elastomers represents a new type of composites, consisting of small (mainly nano and micron‐sized) magnetic particles dispersed in a highly elastic polymeric matrix. The combination of polymers with magnetic materials displays novel and often enhanced properties. Highly elastic magnetic composites are quite new and understanding of the behavior of these materials depending on the composition, external conditions, and the synthesis processes is still missing. Thus, the aim of this work is the study of fundamental principles governing the preparation of these materials as well as their structure and elastic properties. Copyright © 2007 John Wiley & Sons, Ltd.

Novel magnetorheological elastomers (MRE) based on a highly elastic silicone rubber filled with carbonyl iron magnetic particles of 3–5 and 3–50 µm are synthesized. The effect of an external homogeneous magnetic field on the viscoelastic properties of these materials is studied by dynamic experiments (shear oscillations on a rheometer). It is shown that the magnetic response of the MRE increases with a decrease of the strain. At 1% deformation both the storage and loss moduli of the new MRE demonstrate a giant response to the magnetic field, namely, an increase of more than two orders of magnitude in both moduli in a field of 300 mT is observed. In addition, these new MREs show a twofold increase of the damping ratio, which is important for their application as tunable vibration absorbers.magnified image

The dynamic modulus and the loss factor of magnetorheological elastomers (MREs) of various compositions and anisotropies are studied by dynamic torsion oscillations performed in the absence and in the presence of an external magnetic field. The emphasis is on the Payne effect, i.e. the dependence of the elastomer magnetorheological characteristics on the strain amplitude and their evolution with cyclically increasing and decreasing strain amplitudes. MREs are based on two silicone matrices differing in storage modulus (soft, G' ∼ 10(3) Pa, and hard, G' ∼ 10(4) Pa, matrices). For each matrix, the concentration of carbonyl iron particles with diameters of 3-5 μm was equal to 70 and 82 mass% (22 and 35 vol%, respectively) in the composite material. Samples for each filler content, isotropic and aligned-particles, are investigated. It is found that the Payne effect significantly increases in the presence of an external magnetic field and varies with the cyclical loading which reaches saturation after several cycles. The results are interpreted as the processes of formation-destruction-reformation of the internal filler structure under the simultaneously applied mechanical force and magnetic field. Impacts of matrix elasticity and magnetic interactions on the filler alignment are elucidated.