Self-excited oscillatory dynamics of capillary bridges in electric fields

We studied the stability of capillary bridges between flat, parallel, and dielectrically coated electrodes as a function of the voltage applied between them. The stability limits of the capillary bridge state and the state consisting of two separated droplets are shifted with respect to ordinary capillary hysteresis at zero voltage. Surprisingly, we found that the system can oscillate periodically between the two states within a certain range of applied voltage and electrode separation. These oscillations could be applied to promote mixing in electrowetting-based microfluidic devices. We present a model based on the balance between interfacial and electrostatic energies, which explains the experimental findings quantitatively