Electrohydrodynamic instabilities and orientation of dielectric ellipsoidsin low-conducting fluids - art. no. 016301

We study the dynamics of an ellipsoidal particle in a weakly conducting die lectric liquid when submitted to a de electric field. At low field intensit ies, the particle long axis is aligned in the field direction. When the fie ld strength is increased, we show that, depending on the initial orientatio n of the particle, there exist two stable orientations: the one with the lo ng axis parallel to the field direction remains possible while a spinning s tate with the long axis perpendicular to the field appears. This last strik ing orientation is due to the finite Maxwell-Wagner polarization relaxation time. For sufficiently high field intensities, each state loses its stabil ity and the particle dynamics becomes chaotic. Those conclusions from the t heoretical model are supported by experimental observations.