Non-linear magnetorheological behaviour of an inverse ferrofluid

The non-linear magnetorheological behaviour is studied of a model system co nsisting of monodisperse silica particles suspended in a ferrofluid. The st ress/strain curve as well as the flow curve was measured as a function of v olume fraction silica particles and field strength, using a home-made magne torheometer. Both curves were found to scale linearly with the volume fract ion and quadratically with the magnetic moment of the silica particles. Aff ine deformation cannot lead to the observed yield stresses. Instead, a bead -rod model is described that gives results closer to what is observed exper imentally. A master curve for the viscosity was obtained by plotting the di mensionless viscosity versus the Mason number, Mn. The free single chain mo del of Martin and Anderson does not give a good description of the measured curves. This may be due to the simplifications with respect to the microst ructure of and processes in the suspension.