Easy Generation of Droplets in a Capillary Inserted Microchannel

Droplet microfluidics has received increasing attention over the past decade. This study proposes an easy method for droplet generation in microchannels by inserting a glass capillary into a microfluidic chip at required positions. The influences of the capillary insertion depth (0, 60, and 120 μm), capillary inner diameter (50, 75, and 100 μm), and two-phase flow rate ratios (2–12) on the generated droplet length were investigated. The evolution of the two-phase interface during droplet formation is observed in detail, which undergoes three successive stages: head formation, head filling, and neck breakage. Three neck breakage modes were identified as the squeezing, transition, and dripping modes, and the forces acting on the droplets were analyzed. The results show that the proposed capillary-based method can facilitate the generation of droplets in fabricated microfluidic chips over a wide range of two-phase flow rate ratios.