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Magnetoviscous and viscoelastic phenomena in ferrofluids are intimately related to their internal structures. The available kinetic models describing the rheological behaviour rely on strong assumptions and simplifications of these structures. Using equilibrium and nonequilibrium computer simulations, here we discuss the validity of the crucial assumption of rigid, chain-like aggregates underlying the chain model. The simulation results support the existence of chain-like aggregates in strongly interacting ferrofluids, at least for sufficiently strong magnetic fields. In addition, shear-induced degradation of the clusters is observed, which apparently is related to strong shear thinning behaviour. For weakly interacting ferrofluids, only slightly anisotropic spatial structures are observed. In this regime, the simulation results of the magnetoviscous effect are in good agreement with the predictions of a dynamical mean-field theory. Further, we explore some first steps towards a unified kinetic model that is applicable in both, the weakly and strongly interacting regimes.

Magnetorheological elastomers (MRE) are particulate composite materials, whose fillers are structured by a magnetic field during curing. These particles are brought in quasi-contact by the field, in a chain-like unidirectional structure. Due to this organization the local stresses between the particles is high and debonding between particles and elastomer occur at low strain. We have experimentally studied and analytically modeled the progressive breaking of the polymer-to-particle bonds. The two cases of strong and weak bonds between elastomers and particles have been studied. The analytical model correctly reproduces the stress strain curve in the presence of a debonding process although overestimating the size of the debonding cavity which is obtained by comparison between experiments and FEM simulations. The extension of the model to a chain of spheres allows to well explain the Mullins effect on MRE. Furthermore it is shown that the quality of the bonds between the particles and the elastomer does not influence the change of stiffness brought by the application of a magnetic field.

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