Microfluidic production of droplet pairs.

We study a microfluidic dual nozzle for the production of water-in-oil droplet pairs. Droplets are paired by the hydrodynamic coupling of two nozzles over a wide range of aqueous and oil flow rates provided that they are larger than the channel dimensions. The droplet production frequencies and volumes are related to the flow rates through a single, experimentally determined power-law. The data are in good agreement with a model based on a geometrical decomposition of the dual nozzle leading to a general equation of droplet frequencies as a function of the various flow rates.