Deformation mechanisms in 2D magnetic gels studied by computer simulations

Abstract

Magnetic gels, so-called ferrogels, consist of a polymer network, into which magnetic nanoparticles are embedded. The interesting properties of ferrogels originate from a complex interplay of the mechanical properties of the polymers with the magnetic interactions of the embedded nanoparticles. The ability to control the system by an external magnetic field may give rise to applications in medicine and engineering. In this paper, we propose and examine two microscopical simulation models for a 2D ferrogel which are suited to explain two distinct mechanisms of deformation in such a system. The first model focusses on deformation of the gel due to the dipole–dipole interaction between the magnetic nanoparticles. In an external magnetic field, a gel of this kind elongates in the direction parallel to the field and shrinks in the perpendicular direction. The second model deals with a distortion of the polymer matrix due to the transmission of torques from the magnetic nanoparticles to the polymer network. In this model, we observe an isotropic shrinking of the gel in an external magnetic field. As the observed deformations are very different in the two models, we conclude that the magnetoelastic behaviour of a magnetic gel strongly depends on the microscopical details of, both, the structure of the network and the coupling between the polymers and the magnetic nanoparticles. This may help to explain seemingly contradicting evidence from different experiments.