Concentration and composition dependence of rheological and magnetorheological properties of some magnetic fluids

Rheological and magnetorheological behaviour of magnetic fluids with nonpolar and polar carrier liquids were investigated, using capillary and rotary viscometers, the measuring cells being completed with specially designed electromagnets. In the absence of a magnetic field the relative viscosity—hydrodynamicparticle volume fraction dependence is well fitted especially by the formulas of Vand, KriegerDougherty and Chow. The fitted values of the Chow interaction coefficient are close to the theoretical value, except at low temperatures and close packing of magnetic nanoparticles. The effective viscosity of various types of magnetic fluids in an applied magnetic field is strongly dependent on microstructural characteristics. A relatively large, almost 1 order of magnitude, increase in the relative viscosity was measured for medium-concentration water-based magnetic fluids, with large secondary agglomerates. The magnetoviscous effect was found to be rather small, below 10%, for highly stable magnetic fluid samples on decahydronaphathalene and pentanol carriers.