Colloid levitation and Quincke electrorotation in confinement

The Quincke effect is an electrohydrodynamic instability which gives rise to a torque on a dielectric particle in a uniform DC electric field. If a colloid is initially resting on the electrode, it rolls with steady velocity, and the collective dynamics of these Quincke rollers has been subject to a great interest since the pioneering work of Bricard et al, Nature (2013). However, Pradillo et al, Soft Matter (2019) found another regime, where the colloid initially lifts off the bottom electrode and levitates in the space between the electrodes. The lift force is puzzling because the interaction between a charge-neutral sphere and an electrode is always attractive. In this study we theoretically investigate the origin of the repulsive force. We calculate the electrostatic force between a sphere and one or two planar electrodes. Furthermore, we investigate the dynamics of the Quincke rotor in the hovering state and compare it to the dynamics in free space.