Insights Into a Novel Asymmetric T-Type Microdroplet Mixer in the Microfluidic Chip With Tunable Shrink.

A novel microdroplet mixer is proposed by combining the asymmetric offset structure with tunable shrink in the microfluidic chip. The mixer consists of a coaxial flow region in the dispersed-phase channel and an asymmetrical offset aggregation region in the downstream channel, which shortens the mass transfer distance between the solutions to be mixed through the "sandwich" type of initial distribution, and utilizes the tunable shrink to reduce the shear force and break the symmetric vortex during the generation of the microdroplets, prolonging the pre-mixing time. Through finite element simulation, the effects of dispersed-phase flow velocity, continuous-phase flow velocity, the relative angles and offset distances between the continuous and dispersed-phases, and the necking width and length of the tunable shrink on the mixing efficiency inside the droplets were investigated. The internal mixing inside the microdroplet decrease with the dispersed-phase flow velocity, whereas the increase of the continuous-phase flow velocity favors the mixing enhancement. By optimizing the above-mentioned effects, the mixing efficiency achieves as high as approximately 97%, demonstrating the excellent mixing inside the microdroplets in the novel asymmetric micromixer. The proposed microdroplet mixer illustrates advantages of rapid mixing, simple patterned geometry, and easy to fabricate, demonstrating a promising technique for flexibly fluid mixing inside the microdroplet on a microfluidic chip.