Dynamics of droplet generation in a wedge-shaped step-emulsification microchannel

Abstract

The droplet generation in a wedge-shaped step-emulsification microchannel is investigated experimentally and the generation dynamics of dripping flow as a main applicable flow regime is primarily studied. The sodium alginate aqueous solution and liquid paraffin are used as dispersed phase and continuous phase respectively. The droplet generation process is divided into four stages: two-dimensional retracting stage, two-dimensional spreading stage, three-dimensional necking stage, and three-dimensional pinch-off stage. The head of the dispersed phase retracts and spreads faster under higher dispersed phase flow rate or viscosity. The critical neck width between the necking and the pinch-off stages is independent of the dispersed phase flow rate and viscosity. With the increase of dispersed phase flow rate, the droplet size increases while its formation period decreases. The droplet size and formation period increase with the increase in the dispersed phase viscosity. The flow regime of droplet generation relies primarily on the flow rate ratio and viscosities. A correlation is proposed for predicting the droplet size.