Quincke Oscillation of Colloids at Planar Electrodes

Dielectric particles immersed in a weakly conducting liquid are known to exhibit spontaneous rotational motion under uniform DC electric fields above a critical magnitude. So-called Quincke rotation near a planar substrate leads to particle translation and provides a useful experimental model for studying the collective dynamics of active colloids. Here, we show that individual Quincke rollers at planar electrodes can also exhibit oscillatory dynamics, whereby particles move back and forth about a stationary location. The transition from steady rolling to oscillatory motion occurs at a critical field three times larger than that required for rolling. In contrast to previous reports of oscillatory Quincke dynamics based on inertial effects, our observations of micron-scale particles are characterized by low Reynolds numbers (Re ～ 0.01) and therefore negligible inertia.We propose a plausible explanation for Quincke oscillations using the leaky-dielectric model and accounting for electric (and hydrodynamic) interactions of the particle with the conductive substrate.