A novel generator for the preparation of monodisperse femtoliter droplets at high frequency

It has been experimentally demonstrated that droplets, as tiny as 2 μm in diameter, can be generated at rates as high as 20 kHz, with much lower flow rates than needed in the case of conventional flow focusing. The configuration for generating such small droplets consists of a capillary cross, with an exit orifice inserted into the disperse phase channel. With such a structure, the interface of two immiscible fluids is deformed to a shape like Taylor cone. Upon its formation, tiny droplets are issued from the cone tip. This method is found to be highly stable across the flow rate ratios of external to internal fluids, 1～60. By manipulating capillary inner diameters, tip diameters and tip positions, as well as the flow ratio, one can effectively produce droplets in various sizes.