Simulation of structures and their rheological properties in electrorheological fluids

The viscosity of electrorheological (ER) fluids can be changed drastically by imposing an external electric field. We study the relation between microstructures of ER fluids and their viscosity change by performing Stokesian dynamics simulations of a model ER system both in a quiescent state and in a simple steady shear. From large-scale three-dimensional simulations, it is found that (1) under no shear flow there are two principal phases in structural changes: first aggregation of particles into chains oriented along the field direction, and the subsequent slow coalescence of chains into columns, and (2) under a simple steady shear there are three stages in viscosity changes with increasing the field: Newtonian at a weak field, non-Newtonian at a moderate field, and Bingham plastic with yield stress at a high field.