S0520304 ナノ・マイクロ粒子混合系MR流体のMR効果向上と粒子カラム挙動

Abstract

Magnetorheological (MR) fluids are suspensions of micron-sized magnetic particles dispersed into carrier oils, and behave like a Bingham fluid with magnetic-field responsive yield stress. In this research, bidisperse MR suspensions consisting of micro (6.6 μm) and nano (110 nm) iron particles dispersed into silicone oil were fabricated to investigate the enhancement of the MR effects in close relation to the magnetic field-induced particle cluster structures in the static condition and particle column behavior in the shear flow mode. The static particle cluster structures formed in the suspensions under applied magnetic fields were visualized using an optical microscope in a transmission mode, and the particle column behavior in the shear mode was visualized using a hand-made shear flow device and a digital video system with a micro-lens. The MR effects of the bidispersed MR suspensions changed significantly as a function of the solid fraction of nano-particles. Interestingly, the field-induced shear stress was significantly enhanced when the solid fraction of nano-particles was 25%. As well known, the particle chains formed roughly along to the applied magnetic field were observed for the MR suspension containing the micron-sized iron particles. The enhancement of the MR effects can be attributed to the static formation of distinct and wide particle cluster chains reinforced with nano-particles, and the breaking and reconnection of many thicker particle columns in the shear flow mode.