title: Rheological Properties and Stabilization of Magnetorheological Fluids in a Water-in-Oil Emulsion.
abstract: The rheological properties and dispersion stability of magnetorheological (MR) fluids consisting of hydrophilic treated carbonyl iron particles dispersed in a water-in-oil emulsion were studied for the first time by the use of a stress-controlled rheometer and sedimentation test. In order to improve the stability of the MR fluids, carbonyl iron magnetic particles were chemisorbed by Tween 80 and a water-in-oil emulsion was employed as a continuous phase for MR fluids. Attraction between hydrophilic-treated carbonyl iron and water emulsion in continuous phase plays a critical role in greatly improving stability of dense carbonyl iron particles against sedimentation without restricting rheological properties. On application of magnetic fields, the suspensions show a striking increase in viscosity. Since constant stress is generated within the limit of zero shear rate, the plateau in the flow curve corresponds to the Bingham yield stress. Under a low external magnetic field, the yield stress varied as B(3/2), indicating that local magnetization saturation occurs between the neighboring magnetized particles. The yield stress has an approximately linear relation to the particle volume fraction. Copyright 2001 Academic Press.
authors.affiliation: Center for Advanced Functional Polymer (CAFPoly), Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon, 305-701, Korea
authors.forename: Jong Hyeok
authors.initials: JH
authors.lastname: Park
authors.forename: Byung Doo
authors.initials: BD
authors.lastname: Chin
authors.forename: O Ok
authors.initials: OO
authors.lastname: Park