HYSTERESIS PHENOMENON IN FLOW-CURVES OF ER FLUIDS CONTAINING SULFONATED POLYMER PARTICLES

Abstract

The ER fluids containing sulfonated polymer particles were continuously sheared at increasing and decreasing shear rates using a rotary concentric cylinder rheometer and the hysteresis in the up- and down-flow-curves were analyzed. The ER fluids show hysteresis of shear stress and current density. The up-curve (when shear rate increased) was located below the down-curve (when shear rate decreased). As the electric field increased, the area in the hysteresis curves increased. The hysteresis depended on the electric field strength, the time of the applied electric field, the volume fraction of particles and the water content of the particles. Hysteresis phenomenon was explained, based on the formation of agglomerations of dispersed particles in the ER fluid and on changes of the lamellar formations