RHEOLOGY OF A MAGNETORHEOLOGICAL FLUID

We report on experimental investigations of the rheological behavior o f aqueous magnetic suspensions. The suspended particles are monodisper se colloidal polystyrene spheres which contain magnetic Fe2O3-grains. In the absence of a magnetic field these suspensions behave as Newtoni an fluids, whereas under the influence of a magnetic field due to the formation of an ordered structure the apparent viscosity of the suspen sion increases up to three orders of magnitude and they clearly exhibi t non-Newtonian properties, such as shear thinning and yield stress. T he apparent viscosity depends on the magnetic field according to eta s imilar to H-2 Delta. Increasing the volume fraction of the particles i n the range of 0.014 < phi < 0.12 results in a linear increase in appa rent viscosity and yield stress. Both apparent viscosity and yield str ess depend also on the particle size as first measurements on particle s with diameters ranging from 0.5 mu m to 1.0 mu m clearly show. All m easurements were carried out with a rotation viscometer using the cone -plate configuration so that the applied shear rate was well defined.