扁平ヘマタイト粒子の単純せん断流中での配向特性と輸送係数に関する研究

Abstract

We have developed the basic equation of the orientational distribution function of oblate spheroidal hematite particles that conduct the rotational Brownian motion in a simple shear flow under an applied magnetic field. An oblate spheroidal hematite particle has an important characteristic that it is magnetized in a direction normal to the particle axis. Since a dilute dispersion is addressed in the present study, we have taken into account only the friction force (torque) with neglecting the hydrodynamic interactions among particles. This basic equation has been numerically solved in order to investigate the dependence of the orientational distribution on the magnetic field strength, shear rate and rotational Brownian motion, and also the relationship between the orientational distribution and the transport coefficients such as viscosity and diffusion coefficient. The results obtained here are summarized as follows. If the magnetic field is more dominant, the particle inclines such that the oblate surface aligns in the magnetic field direction. If the Peclet number increases and the shear flow becomes more dominant, the particle inclines such that the oblate surface tildes in the shear flow direction. The viscosity due to the magnetic torque increases as the magnetic field becomes strong, since the magnetic torque due to an applied magnetic field becomes more dominant. Moreover, the viscosity increases more significantly for a larger aspect ratio or for a more oblate hematite particle. In another sedimentation phenomenon (not a simple shear flow) where the particle sediments under a magnetic field applied in the sedimentation direction, the particle comes to sediment more significantly with the oblate surface aligning in the sedimentation direction as an applied magnetic field increases.