Generation of monodisperse micro-droplets within the stable narrowing jetting regime: effects of viscosity and interfacial tension

Abstract

In this work, the droplet generation mechanism was comprehensively studied in a modified step T-junction microfluidic device over a wide range of continuous-to-dispersed viscosity ratio. Different surfactant concentrations were utilized to investigate the effect of interfacial tension on the emulsification. Depending on the flow conditions, the droplet generation in the modified step T-junction microchannel can be categorized into dripping, stable narrowing jetting and unstable narrowing jetting regime, where highly monodisperse micro-droplets were observed in the first two regime. The effects of interfacial tension and dispersed liquid viscosity on the micro-droplet generation, notably on the transition from stable to unstable narrowing jetting regimes, were investigated in details. Numerical simulations were conducted to deepen the understanding on the physics behind it. Overall, this work aims to provide a comprehensive guidance for the generation of monodisperse micro-droplets with highly viscous liquids, which is insightful for the fabrication of functional materials in diverse fields.