Electro-rheological fluids:
- What are the equilibrium phases vs. electric field, particle concentration?
- What is the time development of the structures vs. electric field, particle concentration?
We have studied the electric field induced structures in ER suspensions in the absence of shear fields.
Question:
The equilbrium structures have been calculated by Tao and Sun, Phys.Rev.Lett. 67,399 (1991), by treating the particles as point dipoles and minimizing electrostatic free energy. They calculate the equilibrium structure to have a body centered tetragonal (BCT) unit cell. Two views of the BCT structure are shown below.
|
|
|
|
Looking in a plane parallel to the electric field - there is hexagonal order here with the spheres arranged as chains parallel to the E-field and with adjacent chain offset by a particle radius. |
Looking in a plane perpendicular to the electric field - The spheres marked by crosses and dots in the field are indicated in this view. Chains of spheres parallel to the E-field can be seen to have a square-like arrangement. |
Question:
As indicated in the schematic diagram above, the system can go through several metastable states before reaching its equilibrium state.