Inhibition of droplet clustering in step emulsification using deterministic lateral displacement

Abstract

Step emulsification is widely used for microfluidic droplet generation. In step emulsification, however, the accumulation of droplets near the nozzles can cause their coalescence, deteriorating the monodispersity of the product. Here, we propose a method for inhibiting droplet clustering near the step-emulsification nozzles by arranging deterministic lateral displacement (DLD) microposts. The opening width and the height of the nozzles were 124 um and 14 um, respectively. The diameter, the gaps, and the height of the posts were 52 um, 48 um, and 109 um, respectively. Critical diameter of the post array was 40 um. Corn oil and 2 wt% polyvinyl alcohol (PVA) solution were used as the disperse phase and the continuous phase, respectively. The main droplets having diameters of ~ 53 um and satellite droplets having diameters of ~ 4 um were generated at the edges near the nozzles. Then, the main droplets migrated across the DLD micropillar array with a small angle away from the nozzles, while the satellite droplets flowed along the flow direction.