Experimental Studies and Modeling of Temporal Evolution of Chain Formation in Magnetorheological Fluids*

Magnetorheological (MR) fluids are used in a variety of applications due to their formation of chains in an applied magnetic field, but the exact mechanism through which this occurs is unknown. We present results on the time dependent chain formation in a magnetorheological (MR) fluid subject to an applied magnetic field fluid using optical microscopy. We compare the experimental results to a simple model that provides an explanation for the chain formation. The samples consisted of irregularly shaped iron particles with an approximate diameter of 150 microns with concentrations between 0.3% and 2.3% by volume in a carrier fluid of corn syrup. The applied magnetic fields were between 1 and 10 kA/m. The chain lengths, widths, and spacing between chains were recorded optically as a function of time. After 30 minutes in an applied magnetic field, the measured lengths and widths were plotted against the particle concentration and applied magnetic field strength. Notable features include that for a given particle concentration, the measurements were only slightly magnetic field dependent. The chain lengths and widths increase with particle density. A simple simulation of the time dependent chain formation was developed to model the motion of magnetic particles is a viscous fluid with an applied magnetic field. The geometry of the simulated chains gave similar results to the experimental data.