(179t) Influence of the Spin Rotational Brownian Motion On the Magneto-Rheological Effect In a Rod-Like Hematite Particle Suspension In a Simple Shear Flow

In order to clarify the behavior of a dilute suspension composed of rod-like hematite particles, we have derived the basic equation of the orientational distribution function for a simple shear flow. The behavior is strongly dependent on the direction of a magnetic field, and in the present study a magnetic field is assumed to be applied in the shear flow direction. The equation has been solved numerically in order to investigate mainly the influence of the spin rotational Brownian motion on the orientational distribution, the magneto-rheological effect and the characteristics of magnetization. A prolate spheroidal hematite particle has an important characteristic that it is magnetized in a direction normal to the particle axis. Hence, the orientational distribution function depends not only on the particle direction but also on the magnetic moment direction. This implies that the spin rotational Brownian motion about the particle axis has to be included in the basic equation in addition to the ordinary rotational Brownian motion. The main results obtained here are summarized as follows. The present results are in good agreement with those of the theory without that motion in that the position and the height of a peak of the orientational distribution and also the whole distribution shape agree significantly well with each other. Hence, it is seen that the spin rotational Brownian motion does not significantly influence the orientational distribution. In contrast, the spin rotational Brownian motion has a quantitative effect on the viscosity, although the dependence of the viscosity on the magnetic field strength is in qualitatively good agreement with that of the theory without the spin rotational Brownian motion. Moreover, the magneto-rheological effect can be obtained more significantly for a larger aspect ratio or for a more prolate hematite particle. Since the magnetization has a strong relationship with the orientation of the magnetic moment, the effect of the spin rotational Brownian motion appears in this characteristic more significantly.