Robust generation of monodisperse droplets using a microfluidic step emulsification device with triangular nozzle

In this work, the droplet generation process in the microfluidic step emulsification chip with a triangular nozzle (SE-T) was investigated in the combination of visualization experiment and numerical simulation, through a comparison with a rectangular nozzle (SE-R). The flow regimes, including dripping, dripping-jetting transition, and jetting, were observed in the SE-T, among which the dripping is the preferred flow regime to generate monodispersed droplet with corresponding C.V. (coefficient of variation) of the droplet size smaller than 1.9%. Compared with the SE-R, the larger space and expanding structure of the triangular nozzle in the SE-T enhance the wall wetting effects, which induces earlier appearance and accelerates shrinking of the neck. As a result, the SE-T exhibits more robust droplet performance under the dripping regime, which produces the droplets with nearly unchanged size and higher monodispersity, especially little related to the variations of surfactant concentrations and dispersed phase flow rates.

Automated summary

The droplet generation process in the microfluidic step emulsification chip with a triangular nozzle (SE-T) was studied through visualization experiments and numerical simulations, compared to a rectangular nozzle (SE-R). Different flow regimes, including dripping, dripping-jetting transition, and jetting, were observed in SE-T, with dripping being the preferred regime for generating monodisperse droplets. The larger space and expanding structure of the triangular nozzle in SE-T enhanced the wall wetting effects, leading to earlier appearance and faster neck shrinking. Consequently, SE-T showed more robust droplet performance, producing droplets with consistent size and higher monodispersity, regardless of variations in surfactant concentrations and dispersed phase flow rates.