Nonequilibrium cluster structures formed in a thin magnetorheological fluid layer subjected to a dc magnetic field

Tomofumi Ukai,Toru Maekawa,Hisao Morimoto,Jun Dong

doi:10.1063/1.5144574

Abstract

We experimentally investigate cluster structures formed by paramagnetic particles in a thin magnetorheological (MR) fluid layer, the thickness of which normalized by the particle diameter ranges from 3.8 to 31, under a dc magnetic field perpendicular to the fluid layer. We particularly focus on cluster structures formed in a dc magnetic field of high ramping rates, in which case the structures may be greatly different from those formed under equilibrium conditions. When a dc magnetic field is applied so rapidly, paramagnetic particles form chain clusters along the field direction as expected, but some chain clusters coalesce in the lateral direction to form bent-wall structures. We analyze the dependence of cluster structures on experimental parameters such as the thickness of the MR fluid layer and the intensity of the magnetic field.

Highlights

INTRODUCTIONScitation.org/journal/adv between 11 and 22, which is within the range of L/d considered in the present study
A magnetorheological (MR) fluid is a colloidal solution composed of paramagnetic particles dispersed in a carrier fluid such as water or oil.1–3 When an MR fluid is subjected to a dc magnetic field, a magnetic dipole moment is induced in each particle, and linear chain clusters are formed along the field direction due to dipole–dipole interactions between the particles.4,5 the chain clusters composed of paramagnetic particles coalesce in the lateral direction to form various secondary structures under certain conditions
When a dc magnetic field is applied rapidly compared to the relaxation time for the creation of equilibrium structures, magnetic particles are trapped at positions corresponding to the local potential energy minima and form nonequilibrium cluster structures, that is, single chains, columns, bent walls, and labyrinths

Summary

INTRODUCTION

Scitation.org/journal/adv between 11 and 22, which is within the range of L/d considered in the present study. The information about nonequilibrium cluster structures formed by magnetic particles obtained in the present study may be useful for such biological applications of magnetic particles since cell sorting efficiency and DNA separation characteristics may change depending on the cluster structures. We observe cluster structures formed in a thin MR fluid layer under a dc magnetic field, the direction of which is perpendicular to the fluid layer, using an optical microscope and perform digital image analysis to characterize the cluster structures. We carry out a laser diffraction experiment to estimate the average spacing between clusters in the direction parallel to the fluid layer.

Sample preparation

Sample cell

Experimental procedure

RESULTS AND DISCUSSION

CONCLUSIONS