The rotary electrorheological effect

The viscous response of electrorheological fluids is usually manipulated through the use of DC or uniaxial AC electric fields. The result is that fibrillated structures parallel to the field form in a quiescent fluid; the distortion of such structures in a flow determines the enhanced viscous response, at least at low and moderate flow rates. We have conducted preliminary studies of electrorheological response in a different field configuration-a rotating electric field. With respect to the uniaxial AC case, there are two new developments in this type of field. The structures formed are disk-like, in the plane of the rotating field. Furthermore, the structures rotate either with or against the field, depending on the dielectric or conductivity contrast with the surrounding fluid.