Microfluidic Coupling of Step Emulsification and Deterministic Lateral Displacement for Producing Satellite-Free Droplets and Particles

Abstract

Step emulsification, which uses a geometry-dependent mechanism for generating uniformly sized droplets, has recently gained considerable attention because of its robustness against flow fluctuations. However, like shear-based droplet generation, step emulsification is susceptible to impurities caused by satellite droplets. Herein, we demonstrate the integration of deterministic lateral displacement (DLD) to separate the main and satellite droplets produced during step emulsification. Step-emulsification nozzles (16 μm deep) in the upstream region of the proposed device were arrayed on the sidewalls of the main channel (91 μm deep). In the downstream region, the DLD micropillars were arrayed periodically with a critical diameter (cut-off value for size-based separation) of 37 μm. When an acrylate monomer and aqueous polyvinyl alcohol solution were infused as the dispersed and continuous phases, respectively, the nozzles produced monodisperse main droplets in the dripping regime, with an average diameter of ~60 μm, coefficient of variation (CV) value below 3%, and satellite droplets of ~3 μm. Upon entering the DLD region near the sidewall, these main and satellite droplets were gradually separated through the pillars based on their sizes. Finally, off-chip photopolymerization yielded monodisperse polymeric microspheres with an average diameter of 55 μm and a CV value of 2.9% (n = 202).

Microfluidic Step Emulsification with Parallel Nozzles on a Vertical Slit

“…Nongravity-based techniques have also been explored to mitigate droplet accumulation in step emulsification processes. One approach involves elevating the flow rate of the crossflowing continuous phase stream to address droplet accumulation and coalescence issues . However, an indiscriminate increase in the pressure gradient of the continuous phase stream may lead to nonuniform disperse phase flow rates across nozzles, potentially deactivating upstream nozzles and consequently compromising droplet size distribution and production throughput .…”