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 she ar field on a suspension of polarizeable or ER active particles. It demonst rates that the elementary particles in an electrorheologically active suspe nsion, when the suspension is under flow and simultaneously under the influ ence of a large electric field, organize into tight packed lamellar formati ons, the type and orientation being related to the shear field or type of d evice imposing the shear field. These formations resemble walls between par allel plates, cylinders between parallel disks, and disks between concentri c cylinders. In all cases, the columns making up these formations are orien ted in the field direction. When exposed to a field but not under flow, the particles assemble together into numerous columnar like clusters of simila r diameter (100-200 mu m), which an uniformly but randomly distributed betw een the electrodes and oriented in the field direction. Flow alone in the a bsence of an electric field produces no segregation of the elementary parti cles in the suspension. An alternative model for the electrorheological phe nomenon is proposed. (C) 1999 The Society of Rheology. [S0148-6055(99)01405 -4].