Experiment and prediction of droplet formation in microfluidic cross-junctions with different bifurcation angles

Abstract

A visualization experiment was conducted to study the formation of droplets in the cross-junctions with various bifurcation angles. The squeezing, dripping, jetting, and threading without droplet formation were observed, as well as the corresponding detailed droplet formation behaviors and performance were analyzed. A regime diagram was provided to characterize the droplet formation regimes for different bifurcation angles, with the corresponding power-law equation to quantitatively describe the boundaries between different regimes. It is indicated that the variation of bifurcation angle mainly alters the fluid dynamics at the junction, which significantly affects the morphology evolution, hydrodynamic behaviors, droplet size, and regime transition under the squeezing and dripping regimes. In addition, a modified equation considering the significant effect of bifurcation angle was provided and validated to predict the droplet size in the squeezing regime, and the predictive results correlate well with reported results with the relative error that less than ±30%.