Asymmetric branch selection and splitting of droplets in T-junction microchannels

The droplet motion in the T-junction is the basis for the design of droplet microfluidic chip. This paper investigates droplet motion in T-junction microchannels based on experiments and simulations to analyze the droplet motion mode and its effect on the downstream flow of the channel. The droplet motion can be divided into three modes, including flowing into the downstream main channel, flowing into the side branch, and splitting, whose transitions depend on the inlet flow ratio and droplet length. The critical droplet length, to determine whether the droplet is complete through the junction, follows a non-linear relationship of capillary number with the coefficient of 0.3–0.5, which is influenced by the liquid viscosity ratio. It was found that the droplets can be divided into two kinds according to its length by l0 = 0.8wm, which have significantly different interfacial deformations and cause various fluctuations of the branch flow even under the same flow conditions.