The dynamic viscoelasticity of ER suspensions depends on the fluid strain amplitude, the oscillation frequency and the applied electric field strength. This behavior can be explained based on the formation and deformation of ER particle clusters that span the electrodes. In this work, changes of the fibrous structure of an ER fluid in an oscillatory slit flow are analyzed (by direct observation using an optical microscopic probe) when the electric field, the strain amplitude and the oscillation frequency are varied. The ER fluid studied in this work is composed of sulfonated polymer particles (5 vol%) in a silicone oil. The hysteresis loop of pressure difference as a function of strain is explained based on the visualization of the chain-like microstructure.
