A new magneto-rheology device (MRD) was constructed, which can be used in combination with a Physica MCR roational rheometer form Anton Paar. The MRD is build around a parallel-plate measuring geometry. Maximum magnetic flux densities of up to 1 Tesla in the air gap between the two plates are possible. The distribution of the magnetic flux density in the measuring gap has been evaluated with the help of a three-dimensional Hall sensor. The MRD system allows simultaneous software controlled setting of the magnetic field strength and the use of all possible rheological test modes of the rheometer. In the past mostly flow curves based on purely rotational measurements have been used to investigate the rheological behavior of MRFs giving only limited information. A measuring method is introduced, which is based on oscillatory measurements and thus allowing an exact determination of a substance's visco-elastic properties as a function of the magnetic field strength. In addition to structure investigations at various magnetic field strength with standard oscillatory strains sweeps an oscillation measurement with constant amplitude and constant frequency was performed while changing the magnetic field strength in a logarithmic ramp (magneto-sweep). On a typical MRF significant transition points are observed which distinguish different regions. These transitions can directly be correlated to corresponding changes in the material's structure resulting from the increase in the magnetic flux density.
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Laeuger et al. (2005) studied this question.
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