Separation of main and satellite droplets in a deterministic lateral displacement microfluidic device

A microfluidic droplet generator (MFDG) normally produces satellite droplets through break-off from the main droplet because of the Plateau-Rayleigh instability, resulting in contamination and/or poor size distribution of the products. Thus, we herein demonstrate the continuous, passive, and size-based separation of main and satellite droplets using the deterministic lateral displacement (DLD) array method. For the purpose of this study, we designed and employed microfluidic devices comprised of an upstream symmetric flow-focusing MFDG and a downstream DLD array composed of polydimethylsiloxane (PDMS). Initially, we produced water-in-oil (W/O) droplets containing main droplets of ∼61.1 μm diameter in addition to satellite droplets of 1-30 μm diameter in a hydrophobic MFDG, and we report the successful separation of the main and satellite droplets through a single-step DLD array with a critical diameter (D_c) of 37.1 μm. Furthermore, we demonstrated the generation and separation of single-phase or biphasic (i.e. Janus or core-shell) oil-in-water (O/W) main and satellite droplets using a hydrophilic MFDG and a DLD array. Finally, in addition to the removal of main and satellite W/O droplets, we also fractionated satellite droplets of different sizes into three groups (i.e., 21.4, 10.1, and 4.9 μm average diameter) using a device with three-step DLD arrays each having different D_c values (i.e., 37.1, 11.6, and 7.0 μm).