Influence of magnetic particles aggregation on rheological properties

Abstract

The magnetic particles can form aggregates because of magnetic forces, which will cause the change of rheological properties of magnetic fluid. The viscosity of the magnetic fluid and the starting torque of the sealing device were measured in experiments, the results shown that the viscosity and the starting torque are closely related to the aggregates, in addition, shear rate, magnetic field intensity, temperature and standing time are important factors affecting the formation of aggregates. The interaction theory of magnetic particles shown that magnetic particles can spontaneously form unstable aggregates without magnetic field, while aggregates formed in magnetic field have more stable structures. If the magnetic field increases gradually from zero, the spontaneously formed aggregates will undergo a process of destruction and reconstruction, eventually grow into stable aggregates, at the same time, the single domain particles will also be gathered into new aggregates.