Electrorheological Fluid

What looks like a very gory vial of blood is in fact an electrorheological (ER) fluid: a liquid that consists of a suspension of very fine semi-conducting particles in an electrically-insulating fluid (usually silicone oil). When an electric current is put through this liquid, its viscosity changes from the consistency of a liquid to that of a gel in milliseconds, and reverts back when the current is removed. Unlike our sample of MR fluid, this ER fluid has not settled and solidified. This could be because the makers of this substance matched the densities of the suspended particles and carrier liquid so they wouldn’t separate out, or it could be that the suspended particles are nanoparticles (i.e. so small that they are kept suspended by ‘Brownian motion’, as a result of randomly bumping into the moving molecules of the oily carrier medium).