SIMULATION OF THE DYNAMIC OSCILLATORY RESPONSE OF ELECTRORHEOLOGICAL SUSPENSIONS - DEMONSTRATION OF A RELAXATION MECHANISM

The dynamic oscillatory response of electrorheological suspensions is investigated using a molecular dynamics-like simulation method, where suspensions are modeled as hard, monodisperse, neutrally buoyant, dielectric spheres contained in a dielectric, Newtonian fluid between parallel-plate electrodes. The response is described by frequency-dependent moduli, which display a significant relaxation due to competition between hydrodynamic and electrostatic forces on spheres within thick clusters. For small amplitude deformation of monodisperse suspensions, the direct electrostatic contribution to the response obeys time-electric field strength superposition analogous to time-temperature superposition in polymer rheology. The response for monodisperse suspensions is dominated by a single relaxation time, in contrast to the broad dispersions commonly observed. Possible explanations for this discrepancy are discussed.