An easy droplet-generation method using an inserted glass capillary into a microchannel

Abstract

Abstract Droplet microfluidics have received increasing attention over the last decade. This study proposes a facile method for droplet generation in microchannels by vertically inserting a glass capillary into a microfluidic chip. The influences of the capillary insertion depth (0, 60, and 120 µm), capillary inner diameter (50, 75, and 100 µm), and two-phase flow ratios (2–12) on the generated droplet length are investigated. The morphology evolution of the two-phase interface during droplet formation is given in detail, which undergoes three successive stages: head formation, head filling, and neck breakage. Three breakage modes for the droplet neck are identified as the plunger, squeezing, and dripping modes, and the forces acting on the droplets are analyzed. The results indicate that the proposed method can generate droplets stably and robustly. The size is accurately controlled to readily provide droplet generation in microchannels.