Formation of Nanoliter Droplets in a Confined Microfluidic T-Shaped Junction: Formation Time and Droplet Volume

Nanoliter droplet formation in a confined T-shaped junction is analyzed in detail in virtue of an experimental visualization system with a high speed camera. The movement of the back interface of the tip of disperse phase penetrated into the continuous phase plays an important role in determining droplet formation time and droplet volume. A simple model of droplet formation time based on the analysis of droplet formation process is developed. Influences of continuous phase viscosity and interfacial tension on droplet formation time and droplet volume are concluded in terms of capillary number together with the mean velocity of continuous phase. It is found that both the capillary number and the flow rate ratio of disperse phase to continuous phase have strong impacts on determining droplet volume. Two empirical equations are derived from the model for predicting droplet formation time and droplet volume, respectively.