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Magnetorheologische Materialien

(Nano-) Komposite und Blends



M.Sc. Bastian Walter


Tel.: +49 9131/85-27746

Fax: +49 9131/ 85-28321


Raum: 1.90

Magnetorheological Materials (MRMs) are smart materials, whose properties, in particular the rheological and mechanical ones, can be altered significantly and reversibly, applying an external magnetic field. In general, MRMs are composed of a non-magnetic matrix (e.g. oil or rubber) filled with magnetically permeable (e.g. ferromagnetic) particles of micro meter size (typically ø 3-5 µm). By applying a magnetic field, magnetic dipoles are induced. Due to dipole-dipole interactions, the originally randomly distributed particles (Figure 1) build up chain-like structures (Figure 2) oriented in field direction. The properties of the matrix, the size and size-distribution of the particles as well as their composition and volume filler fraction influence the characteristic response of MRMs. In addition, other fillers present in the matrix (e.g. fumed silica), may have an effect on the resulting MRMs as well.



Figure 1: Sketch of particle structure in a MRM without an external magnetic field (B=0).
Figure 2: Sketch of particle structure (strings) in a MRM with an external magnetic field B.


According to the matrix, MRMs are classified into Magnetorheological Fluids (MRFs) and Magnetorheological Elastomers (MREs). MRFs, composed of a non-magnetic, viscous fluid (e.g. silicone oil), were first developed and investigated by Jacob Rabinow, focusing on magnetic fluid clutches, in the late 1940s. Later on, rotary brakes and linear dampers were developed, utilizing MRFs as well. Additionally, other fillers (e.g. fumed silica) may be present, forming a filler network to reduce sedimentation, enhancing the stability of MRFs.


MREs, which were for instance developed at the Ford Research Laboratory (USA), consist of a non-magnetic, rubber-like, polymeric matrix (e.g. silicone or natural rubber). To enhance the mechanical properties of the rubbery matrix, reinforcing fillers (e.g. fumed silica in Liquid Silicone Rubber LSR) may be present, increasing the tensile strength, tear strength and fatigue behavior as well. The formation of structure causes anisotropy in the properties, which can be used in various applications of MREs as sensor and/or actuator.


Focusing on MREs, it is important to understand the influence of material formulation (e.g. polymer, crosslinking density, plasticizer and filler content, etc.) and processing conditions during crosslinking (e.g. temperature, magnetic field, etc.), to optimize their properties. Therefore, model systems are studied by means of a rheometer equipped with a magneto-rheological cell and a universal testing machine allowing the measurement of mechanical properties in a defined magnetic field. μ-CT and SEM imaging are used to control the homogeneity, structure and reproducibility of the composite. Thus, correlations between microstructure and performance are established.