Simple and flexible production of controllable emulsion droplets from open-type co-flow microfluidics

An open-type co-flow microfluidic technique that allows simple microflow manipulation with a broad operation range of flow rates for controllably producing uniform droplets with widely adjustable sizes is developed. The microfluidic device employs a co-flow geometry with relatively open shearing space to largely reduce the pressure drop in the microchannel to facilitate the flow of liquids. Such a device significantly extends the operation window of the dripping regime and eliminates the back flow, to benefit easy microflow manipulation with broadly adjustable flow rates for producing monodisperse droplets with widely tunable sizes. Typically, at Wed = 0.0028, the operation window of the dripping regime and adjustable range of flow rates for this device are both at least ∼3 times wider than those of traditional co-flow devices with confined shearing space for droplet generation. This work provides a facile microfluidic platform with simple flow manipulation and a wide operation range for the wide-scale impact of droplet microfluidics.