Controlling shedding characteristics of condensate drops using electrowetting

We show here that ac electrowetting (ac-EW) with structured electrodes can be used to control the gravity-driven shedding of drops condensing onto flat hydrophobic surfaces. Under ac-EW with straight interdigitated electrodes, the condensate drops shed with relatively smaller radii due to the ac-EW-induced reduction of contact angle hysteresis. The smaller shedding radius, coupled with the enhanced growth due to coalescence under EW, results in increased shedding rate. We also show that the condensate droplet pattern under EW can be controlled, and the coalescence can be further enhanced, using interdigitated electrodes with zigzag edges. Such enhanced coalescence in conjunction with the electrically-induced trapping effect due to the electrode geometry results in larger shedding radius, but lower shedding rate. However, the shedding characteristics can be further optimized by applying the electrical voltage intermittently. We finally provide an estimate of the condensate volume removed per unit time in order to highlight how it is enhanced using ac-EW-controlled dropwise condensation.