単純せん断流中での強磁性棒状粒子からなるコロイド分散系の挙動に関するブラウン動力学シミュレーション : 第1報,磁場がせん断面に垂直な方向に作用する場合(流体工学,流体機械)

Abstract

We have investigated aggregate structures and rheological properties of a colloidal dispersion composed of ferromagnetic spherocylinder particles with a magnetic moment along the particle axis direction, by means of Brownian dynamics simulations. In concrete, we have attempted to clarify the influences of the flow field, magnetic field strength, magnetic interactions between particles and volumetric fraction of particles. In order to discuss quantitatively the internal structures of clusters, we have focussed on the radial distribution and orientational distribution functions. The present results are compared with those of the theoretical analysis for non-dilute dispersions by means of the mean-field approximation. The results obtained here are summarized as follows. For the case of a strong magnetic field and strong magnetic interactions between particles, thick and long clusters are formed along the magnetic field direction. As the influence of the flow field increases from such a situation, those clusters dissociate, and the particles are tilted to the flow direction. Although magnetic interactions between particles influence the orientational distribution function in the case of the mean-field approximation, it does not influence significantly the orientational distribution function in the case of the present study because the torque acts on the particles from the other cluster. For a dilute case, as magnetic interactions between particles increase, many step-like clusters are formed so that the viscosity due to magnetic properties and steric layers significantly increases.