Remarks on microfluidic fabrication of nano-/subnano-liter droplets

In the microchannel-emulsification approach for producing nano-/subnano-liter droplets, the external energy input into the droplet accounts for the variation of the droplet surface free energy during its growth on the terrace. Avoiding the demand for an infinite energy input is the mechanism responsible for the experimental observation that there is always some remaining dispersed liquid on the terrace after generation of one droplet. A better empirical relation exists for correlating the experimental data of the droplet size in the literature. Based on a balance of the surface tension and the drag force, we have also developed a simple scaling model for predicting the size of droplets fabricated in microfluidic T-junctions.