Magnetorheology of submicron diameter iron microwires dispersed in siliconeoil

Abstract

We investigate the magnetorheological (MR) properties of suspensions containingiron microwires with 260 nm diameter and two distinct length distributions of5.4 ± 5.2 µm and 7.6 ± 5.1 µm suspended in silicone oil (0.45 Pa s). The rheological properties of these fluids were determinedusing a parallel plate rheometer equipped with a variable strength electromagnet. Theshear stress was measured as a function of shear rate for increasing applied magnetic fields.These results were modeled using the Bingham-plastic constitutive model to determine theapparent yield stress and viscosity as a function of increasing volume fraction and lengthof microwires. At a saturated magnetic flux density, the yield stress using the5.4 µm microwires was found to be 0.65, 2.23, and 4.76 kPa for the 2, 4, and 6 vol% suspensions, respectively. Forthe 7.6 µm wires, the yield stress increases to 8.2 kPa for the 6 vol% suspension. Compared withconventional MR fluids employing spherical particles, the degree of settling is markedlydecreased in the microwire-based fluids. At 6 vol%, conventional fluids display appreciablesettling whereas the microwire-based fluids display no discernable settling. Moreover, therod-shaped microwires are shown to increase the yield stress of the fluids and enhance theMR performance.