Conclusion and outlook

Abstract

It has been shown, that the viscosity of a suspension of magnetic particles can be strongly influenced by magnetic fields of moderate strength. Particular interest has been devoted to the investigation of commercial ferrofluids, being designed for actual technical applications like loudspeakers or sealings. In a series of experiments we’ve found that the qualitative behavior of the fluids can be described by Shliomis’ theory of rotational viscosity based on the assumption, that the free rotation of the suspended magnetic particles in a shear flow is hindered by the action of magnetic fields. In particular the experiments have been used to verify the general behavior for weak magnetic field, leading to an increase of viscosity proportional to the square of the strength of the magnetic field, and the predictions concerning the dependence of the magnetic field-induced viscosity changes on the mutual direction of the magnetic field and the vorticity of the flow.