The apparent viscosity of these fluids changes reversibly by an order of up to 100,000 in response to an electric field.
For example, a typical ER fluid can go from the consistency of a liquid to that of a gel, and back, with response times on the order of milliseconds.
[3] The change in apparent viscosity is dependent on the applied electric field, i.e. the potential divided by the distance between the plates.
When activated an ER fluid behaves as a Bingham plastic (a type of viscoelastic material), with a yield point which is determined by the electric field strength.
An ER fluid has been constructed with the solid phase made from a conductor coated in an insulator.
They can be ferroelectric or, as mentioned above, made from a conducting material coated with an insulator, or electro-osmotically active particles.
[6] A much larger increase in ER effect can be obtained by coating the electrodes with electrically polarisable materials.
The GER fluid consists of Urea coated nanoparticles of Barium Titanium Oxalate suspended in silicone oil.
Another problem is that the breakdown voltage of air is ~ 3 kV/mm, which is near the electric field needed for ER devices to operate.
Unfortunately, the increase in apparent viscosity experienced by most Electrorheological fluids used in shear or flow modes is relatively limited.
However, an almost complete liquid to solid phase change can be obtained when the electrorheological fluid additionally experiences compressive stress.