Effect of electric field on droplet formation in a co-flow microchannel

The present study investigated experimentally the effect of electric field on droplet formation process in a co-flow microchannel. A silicone oil (viscosity of 4.6 mPa · s) and an aqueous solution (mixture of 52% w/w water–glycerol) were used as the continuous and dispersed phases, respectively, while the applied voltage varied from 0 kV to 10 kV. It was found that both electric field and flow rates of the two phases affected the droplet formation process. When no electric field was utilized, the droplet size decreased with increasing continuous phase flow rate while the formation time decreased with increasing dispersed phase flow rate. When an electric field was applied, both the droplet size and formation time decreased with increasing voltage. Three droplet formation patterns, namely squeezing, dripping, and jetting, were identified. Under the effect of electric field, the range of flow rates where the squeezing pattern appeared reduced. The droplet size was related to the electric Bond number and the flow rate ratio of the continuous phase to the total flow rate with exponents that depended on whether the electric field affected the droplet formation process. A flow pattern map with phase flow rate ratio and electric Bond number as coordinates was also built.