Magnetostriction and piezoresistivity in elastomers filled with magnetic particles

Abstract

Magnetorheological elastomers consist in a dispersion of micron size (typically 1-5μm) magnetic particles inside an elastomer. During curing, the suspension is subjected to a strong magnetic field that creates an attractive force between particles in a direction parallel to the magnetic field, thus arranging the homogeneous dispersion in a chain-like structure. Once the polymer is cured, this unidirectional structure is kept. We shall present some results showing that the adaptive character of the material does not depend on the fact that particles are grafted to the matrix or not, but rather on the volume fraction of particles and above all on their organisation inside the matrix. In particular we shall see that, in addition to the change of modulus in the presence of a field, some very important magnetostrictive effect can also be observed in such composite. We explain this behaviour by the existence of a small layer of elastomer between the magnetic particles. In an other situation, with the use of nickel particles inside the elastomer, the gap between particles is much thinner and a small compression can change the resistivity of the sample by many orders of magnitude making it a very sensitive pressure sensor.