Using an electro-spraying microfluidic chip to produce uniform emulsions under a direct-current electric field

An electro-spraying microfluidic chip was integrated with a parallel electrode and flow-focusing device to successfully generate uniform emulsions with an electric field. This approach utilizes a high electric field driven by a direct-current voltage to form a stable Taylor cone in the flow-focusing position. The Taylor cone can then generate stable and uniform emulsions that are less than 5 μm in diameter. The emulsion size is controlled by the surfactant concentration, the ratio of the water and oil phase flow rates and the strength of the electric field. When the strength of the electric field increases at a high surfactant concentration and low ratio of flow rates, the Taylor angle decreases, which causes the emulsion size to decrease. In this study, the water emulsion diameter ranged from 1 to 98 μm, and the poly(lactic-co-glycolic acid) (PLGA) emulsion size ranged from 7 to 70 μm. The microfluidic chip developed in this work has the advantages of actively controlling the emulsion size and generating uniform emulsions (the relative standard deviation was less than 10%) and represents a new emulsion generation process.