Rheology and structure of a suspension of particles subjected to Quincke rotation

We report some experimental results that show that, if the particles of a suspension rotate faster than the surrounding liquid, the apparent viscosity is lessened. The increase of the particles’ spin rate is induced by Quincke rotation, which is the spontaneous rotation of an insulating particle immersed in a slightly conducting liquid when submitted to a high enough DC electric field. We study the flow of such a suspension with internal spin rate in various geometries, and we observe, depending on the values of the shear rate and of the electric field, that the suspension can form a layered structure or present a decomposition into two phases. To predict the appearance of the layered structure, we propose to introduce a modified Mason number that takes into account the rotation of the particles. Paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29 2006, Crete, Greece.