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Structural deformation in the low shear rate region that is an undeformed state is investigated for the isotropic and anisotropic magnetic particle-based magnetorheological (MR) fluid. Flow curves were obtained for both MR fluids between 0.1 s −1 and 500 s −1 in the absence and in the presence of magnetic fields. A model to describe the flow behavior over the full shear rate study is proposed. The proposed model accounts for the friction contribution coming from particle-particle as well as particle-carrier interactions of anisotropic particles particularly in flake-shaped particles. The parameters derived from the fit have physical meaning, and it correlates with the observed dependency in rheology study. To get a better understanding of particle-particle friction contribution, magnetic nanoparticles were added in the MR fluid and flow behavior is studied. The study clearly demonstrates the contribution of particle-particle friction on the MR properties. The contribution of particle-carrier friction, due to the shape of the particle, is verified by comparing the result with spherical-shaped particle-based MR fluid.

Magnetorheological (MR) fluids were prepared in transformer oil as well as transformer oil based magnetic fluid having 2 wt. % of Fe3O4 particles. The thermal conductivity enhancement (w.r.t. carrier) in the case of transformer oil based MR fluid under a field was found to vary from 219%, 304%, and 356%, respectively, from 15 vol. %, 20 vol. %, and 25 vol. % of iron concentration. These values are much higher than that obtained for spherical-shaped iron particles based MR fluids. This is further enhanced by another 30% at the same magnetic field when the same flakes were dispersed in transformer oil based magnetic fluid. In addition, the magnetic fluid based MR fluids exhibit minimum hysteresis in thermal conductivity when the field is removed. The increase in the thermal conductivity of transformer oil based MR fluid is due to the shape effect as well as the reduction in thermal resistance due to a higher particle-particle interaction compared to spherical particles. In addition, on adding nanoparticles, the friction between the particles reduces and nanoparticles facilitate flake-shaped particles to form a stronger chain. This results in an enhancement in thermal conductivity. The observed reduction in the viscosity of MR fluids with nanoparticles supports the concept of the increased orientation of flakes in the direction of the field.

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