title: Viscoelasticity of suspensions of magnetic particles in a polymer: effect of confinement and external field.
abstract: We study the suspensions of magnetic particles, the precursor state of magnetic gels and elastomers. We use magnetic particles with a permanent magnetization which is high enough to overcome thermal energy and low enough to guarantee a long live time of the sample. These particles form a space-filling structure at very low volume fractions (approximately 0.5 vol %), which modifies the viscoelastic response of the matrix significantly. In confined geometry the particles form clusters of a size that depends on the sample thickness. Even small external fields induce a strong anisotropy in the mechanical and optical properties of the suspension. The action of the applied magnetic field induces a gel-like response in one direction but leaves the other directions liquidlike. The viscosity is a very sensitive mechanical test for the anisotropy of the material. Light scattering data confirm our mechanical results.
authors.affiliation: Institut de Mécanique des Fluides et des Solides, UMR 7507 ULP-CNRS, 2 rue Boussingault, 67070 Strasbourg, France. guenter.auernhammer@mpip-mainz.mpg.de
authors.forename: Günter K
authors.initials: GK
authors.lastname: Auernhammer
authors.forename: Dominique
authors.initials: D
authors.lastname: Collin
authors.forename: Philippe
authors.initials: P
authors.lastname: Martinoty