Flow profiles of electrorheological suspensions: An alternative model for ER activity

This paper shows the effect of the coupling of an electric field with a shear field on a suspension of polarizeable or ER active particles. It demonstrates that the elementary particles in an electrorheologically active suspension, when the suspension is under flow and simultaneously under the influence of a large electric field, organize into tight packed lamellar formations, the type and orientation being related to the shear field or type of device imposing the shear field. These formations resemble walls between parallel plates, cylinders between parallel disks, and disks between concentric cylinders. In all cases, the columns making up these formations are oriented in the field direction. When exposed to a field but not under flow, the particles assemble together into numerous columnar like clusters of similar diameter (100-200 mu m), which an uniformly but randomly distributed between the electrodes and oriented in the field direction. Flow alone in the absence of an electric field produces no segregation of the elementary particles in the suspension. An alternative model for the electrorheological phenomenon is proposed. (C) 1999 The Society of Rheology. [S0148-6055(99)01405-4].