VISCOELASTICITY OF A DIELECTRIC FLUID IN NONUNIFORM ELECTRIC-FIELDS GENERATED BY ELECTRODES WITH FLOCKED FABRICS

The rheological behavior of a dielectric fluid is studied in nonunifor m electric fields which are generated by an electrode covered with flo cked fabrics. Although no electrorheological (ER) effects are observed in uniform fields between metal electrodes with smooth surfaces, stri king increases in viscosity and elastic response are induced by the el ectrode with flocked fabrics. The presence of flocked fabrics does not have a significant effect on the fluid rheology without electric fiel ds. The ER behavior and current density are influenced by the fiber le ngth even at a constant field strength. When a very small amount of fi ne particles is introduced in the electrified fluid without shear, we can see the rapid and large-scale motion of particles between the tips of fibers and plate electrode. In high DC fields, the Coulomb force a cting on a free charge often gives rise to the secondary motion of flu id. The local motion of fluid in high electric fields is refereed to a s electrohydrodynamic (EHD) convection. The additional energy may be r equired to change the periodic patterns of EHD convection by forced sh ear. Therefore, the ER effect demonstrated by the modification of elec trode with flocked fabrics can be attributed to a combined effect of E HD convection and external shear.