A Novel Droplet Sieving Method Using an Array Protrusion Microchannel and Separation Mechanism

A novel droplet separation method was proposed by using an array protrusion microchannel, which could divert droplets of different sizes into designated branch channels. The performance and mechanism of droplet sieving were investigated. In this work, three distinct flow patterns were obtained: partial sieving, complete sieving, and main drop loss regimes. The influences of droplet length and operation conditions on the sieving efficiency were studied systematically. It was found that, in the partial sieving flow pattern, the increase of small droplet diameter is not conducive to sieving, and there exists a critical diameter of the small droplet for complete sieving under a constant main droplet size, which relies primarily on the array protrusion height. The operating range of the complete sieving flow pattern extends when increasing the main droplet size, and the critical capillary number for evolving into the main droplet loss flow pattern rises. The sieving efficiency increases with the flow rate of the continuous phase in the regulating channel while decreasing with that in the main channel.