Droplet separation and sieving mechanism by grooved microchannel

A novel droplet sieving method utilizing grooved microchannel is proposed to achieve the monodispersity of droplets. The sieving performance and mechanism are investigated experimentally. Three different sieving flow regimes are observed in the experiment: incomplete sieving, complete sieving and main droplet rupture. The effects of different operating conditions on sieving efficiency are studied systematically. The results showed that when the total flow rate of the continuous phase in the main channel is lower, the small droplets would accu-mulate between the main droplets and could not be separated. Complete sieving could be achieved when the main body of the small droplet enters the sieving layer before arriving at the sieving channel. The larger continuous phase flow rate in sieving channel could create thicker sieving layer, which is conducive for small droplets to entering the sieving layer to achieve complete sieving. On the contrary, the higher continuous phase flow rate in the main channel would lead to thinner sieving layer, and the required flow rate in sieving channel would be higher to achieve complete sieving. Under the same sieving channel flow rate, the longer droplet is more apt to rupture. The sieving mechanism of droplets is proposed according to the force analysis in the channel. Whether the main droplet ruptures at the sieving junction depends on the combined action of the suction of the sieving channel, the interfacial tension, and the supporting force of the sieving groove.