Dynamic mechanism of double emulsion droplets flowing through a microfluidic T-junction

A microfluidic chip is adopted to study the droplet dynamic behaviors when flowing through the T-junction. Large ranges of initial length (Lo/w = 0.8–2.8), capillary number (Cao = 0.030–0.165), and viscosity ratio (λo = 0.16–5.90) are considered to identify the deformation characteristics and the breakup results. Three flow patterns are categorized in the T-junction, and critical conditions are expressed as power law relations between the normalized length and the capillary number. The coupling competition exists between outer neck thinning and inner droplet shifting, which influences the deformation process. A state diagram indicating the number of breakups is built through two key features of the shifting behavior, namely, the shifting distance and the shifting velocity. With increasing viscosity ratio, thresholds of both breakups decrease due to the reduced deformation resistance caused by vortex flow and the weakened coupling effect, resulting from the suppressed shifting behavior. The shell thickness via twice-breakup pattern depends solely on the viscosity ratio.