Particle behavior in shear and electric fields. VII. Orientation distributions of cylinders

Abstract

Transient orientation distributions of electrically conductive rods and discs in suspensions subjected to combined shear and electric fields were determined experimentally. In subcritical electric fields the orientation distribution oscillated at a frequency twice that of the individual particle's rotation; the orbit distribution drifted towards higher orbits with rods and lower orbits with discs, so that eventually the axes of rods and the faces of discs lay in planes normal to the vorticity axis. In supercritical fields the orientation distributions no longer oscillated, but changed gradually as each particle moved to a steady orientation. Monotonic changes in orientation distributions occurred in suspensions subjected to an electric field alone. All of these observations were as predicted from theory. The influence of electric fields on such rheological properties as the intrinsic viscosity and normal stress differences of the suspensions are discussed.