Electrohydrodynamic Deformation and Rotation of a Particle-Coated Drop

A dielectric drop suspended in conducting liquid and subjected to a uniform electric field deforms into an ellipsoid whose major axis is either perpendicular or tilted (because of the Quincke rotation effect) relative to the applied field. We experimentally study the effect of surface-adsorbed colloidal particles on these classic electrohydrodynamic phenomena. We observe that at a high surface coverage (90%), the electrohydrodynamic flow is suppressed, oblate drop deformation is enhanced, and the threshold for tilt is decreased compared to that of the particle-free drop. The deformation data are explained well by a capsule model, which assumes that the particle monolayer acts as an elastic interface. The reduction of the threshold field for rotation is likely related to drop asphericity.