chains to form columns. The formation of columns with For electrorheological (ER) suspensions, the aggregate strucordered lattice has been theoretically predicted (5,6) and tures of particles were observed in electric fields by the use of experimentally confirmed (7, 8). When the electrified sustransparent cells with different electrode patterns. Although the pension is subjected to shear at low stresses, the energy fed suspension is dispersed to noninteracting particles without electric to column is not elastically stored but is dissipated during fields, many aggregates are formed on the electrode surface in the deformation process. Therefore, the behavior is purely electric fields. Since the dipole-dipole interactions cause chain plastic, and the removal of stress does not results in elastic structures of particles and equilibrium conformations of chains recovery (9, 10). The yield behavior of ER fluids can be are always aligned with electric field, the aggregates indicate the closely related to the deformation of the column rather than presence of columns spanning the electrode gap. The particle concentration in columns which are developed between parallel-plate the individual chain itself. electrodes is about 22 vol %. In striped electrodes, the particles
In a previous paper (11), we have studied the relation construct striped aggregates along the electrodes and no particles between the column structures and rheological properties for remain in the insulating region. The particle concentration in suspensions at particle concentrations below 10 vol %. The striped aggregates is about 35 vol %. The nonuniformity of electric yield stress and, in turn, the column strength rapidly increase field is responsible for the high particle concentration. The increase with increasing column thickness. Even though the total in particle concentration of column lead to the high yield stress number of chains is constant, the yield stress is strikingly of electrified suspension. Therefore, the ER performance of susincreased by the aggregation of chains. The most important pension as an overall response can be improved by the electrode factor determining the rheology of ER suspensions is the design. แญง 1997 Academic Press column structure. In the present paper, the field-induced