Droplet group production in an AC electro-flow-focusing microdevice

We report the production of droplet groups with a controlled number of drops in a microfluidic electro-flow-focusing device under the action of an AC electric field. This regime appears for moderate voltages (500–700 V peak-to-peak) and signal frequencies between 25 and 100 Hz, much smaller than the droplet production rate (∼500 Hz). For this experimental condition the production frequency of a droplet package is twice the signal frequency. Since the continuous phase flow in the microchannel is a Hagen–Poiseuille flow, the smaller droplets of a group move faster than the bigger ones leading to droplet clustering downstream.