Magnetorheological fluids exploiting nanometer-sized particles

Abstract

Magnetorheological(MR) fluids are suspensions of magnetic particles in a carrier fluid. The rheological properties of MR fluids undergo changes on application of magnetic field. MR fluids made using nanometer sized soft magnetic iron particles were studied for their benefits vis-a-vis flow characteristics and settling properties. Three kinds of MR fluids were synthesized using the microwave process (1) 30 micrometers sized iron particles (2) 26.5 nm sized iron particle (3) a mixture of micron and nanometer sized iron particles . The fluids were suspensions of micron, nanometer as well as a mixture of nanometer and micron sized powders. Standard static and dynamic yield stress measurements were performed using a parallel disc oscillatory rheometer. The flow properties of these fluids were then characterized using the Bingham-Plastic, Eyring-Plastic and the Herschel-Buckley models. This paper investigates the rheological properties of these fluids and assesses their advantages and disadvantages. The pure micron powder yielded an MR fluid with highest yield stress, but had the most rapid settling. The nano sized powders overcame the problem of settling because of the predominance of thermodynamic forces at that scale, but they yielded a considerably lower yield stresses. A hybrid combination of micron and nano sized powders was an effective compromise to exploit the high yield stress provided by the micron powders and the self dispersing properties of the nano sized powders. We characterized these mixtures using existing rheological models. A key conclusion is that it may be possible to synthesize MR fluids with significant yield stress, while mitigating settling through the use of nanoscale powders.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.