Shear-dependent microvortices in liquid-liquid flow-focusing geometry: A theoretical, numerical, and experimental study

Abstract

In this work, we describe the mechanism of particle trapping and release at the flow-focusing microfluidic droplet generation junction, utilizing the hydrodynamic microvortices generated in the dispersed phase. This technique is based solely on our unique flow-focusing geometry and the flow control of the two immiscible phases and, thus, does not require any on-chip active components. The effectiveness of this technique to be used for particle trapping and the subsequent size selective release into the droplets depends on the fundamental understanding of the nature of the vortex streamlines. Here, we utilized theoretical, computational, and experimental fluid dynamics to study in detail these microvortices and parameters affecting their formation, trajectory, and magnitude.