Influence of External Magnetic Field Direction on Orientational Distribution and Rheological Properties in a Dilute Suspension Composed of Spindle-Like Hematite Particles (Analysis with Consideration of Spin Rotational Brownian Motion)

Abstract

We have theoretically investigated the particle orientational and rheological properties of a dilute suspension composed of spindle-like hematite particles under a simple shear flow. We have derived the basic equation of the orientational distribution function with spin rotational Brownian motion. The basic equation has been solved numerically in order to investigate the influence of the shear rate, magnetic field strength, and rotational Brownian motion on the orientational distribution and rheological properties. For a very strong magnetic field applied in the shear flow direction, the particle inclines in the direction normal to the flow direction. Also, the particle is restricted in a plane normal to the shearing plane due to the spin rotational Brownian motion. The viscosity becomes large with increasing magnetic field strength. In the case of an external magnetic field applied in the direction of the angular velocity of a simple shear flow, the particle inclines toward a plane normal to the shearing plane, while the magnetic moment is restricted in the direction of the magnetic field. The particle can easily rotate around the magnetic moment under circumstances of a weak shear flow. For a strong shear flow, the particle inclines in the shear flow direction and does not rotate around the magnetic moment. The viscosity due to magnetic properties does not occur under the situation of a magnetic field applied in the direction of the angular velocity vector of a simple shear flow.