<title>Magnetorheological fluids exploiting nanometer-sized particles</title>

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 µ m 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 synthesise MR fluids with significant yield stress, while mitigating settling through the use of nanoscale powders.

Synthesis and characterization of novel flake-shaped carbonyl iron and water-based magnetorheological fluids using laponite and oleic acid with enhanced sedimentation stability

“…However, with enhancing carrier fluids viscosity, in the presence of a magnetic field, the viscosity of MR materials will be decreased. The second was the use of nano-sized particles to replace micro-sized particles because nano-sized particles may suspend more stable than micro-sized particles in the carrier liquid (John et al, 2002;Laun et al, 1996;Phule and Ginder, 1999;Rosenfeld et al, 2002).…”

Rheological Parameter Estimation for a Ferrous Nanoparticle-based Magnetorheological Fluid using Genetic Algorithms

“…Nanometer-sized iron particles, ranging from 10 to 100 nm, were introduced to reduce settling while maintaining useful yield stress levels (Kormann et al, 1992;Taketomi et al, 1993;Rosenfeld et al, 2002). It was shown that the introduction of nanoparticles reduced settling (John et al, 2002;Trihan et al, 2003), but the yield stresses for MR fluids having constant solids loading was reduced when nanoparticles were substituted for micron scale particles in the MR suspension (Poddar et al, 2004;Chaudhuri et al, 2005). However, the shear stresses in these fluids are comparable with shear stresses achieved in conventional electrorheological (ER) fluids and the phenomenon is also seen to be temperature dependent.…”