Preparation of monodisperse emulsions by hydrodynamic size fractionation

We describe a microfluidic system allowing fast and efficient size-dependent separation of droplets using hydrodynamics. This system allows efficient fractionation of droplets with a difference in volume as small as 2.33-fold (corresponding to a 1.33-fold difference in diameter of spherical droplets) at >4.5 kHz frequencies. To demonstrate the utility of the system we combined the size-fractionation module with a passive droplet fusion module to create an integrated microfluidic platform allowing the preparation of highly monodisperse emulsions composed of >99% pairwise fused droplets. This type of microfluidic platform should be useful for many droplet-based lab-on-a-chip applications.