Double emulsion formation through hierarchical flow-focusing microchannel

A microfluidic device is presented for creating double emulsions, controlling their sizes and also manipulating encapsulation processes. As a result of three immiscible liquids' interaction using dripping instability, double emulsions can be produced elegantly. Effects of dimensionless numbers are investigated which areWeber number of the inner phase (We(in)), Capillary number of the inner droplet (Ca-in), and Capillary number of the outer droplet (Ca-out). They affect the formation process, inner and outer droplet size, and separation frequency. Direct numerical simulation of governing equations was done using volume of fluid method and adaptive mesh refinement technique. Two kinds of double emulsion formation, the two-step and the one-step, were simulated in which the thickness of the sheath of double emulsions can be adjusted. Altering each dimensionless number will change detachment location, outer droplet size and droplet formation period. Moreover, the decussate regime of the double-emulsion/empty-droplet is observed in low We(in). This phenomenon can be obtained by adjusting theWe(in) in which the maximum size of the sheath is discovered. Also, the results show that Ca-in has significant influence on the outer droplet size in the two-step process, while Ca-out affects the sheath in the one-step formation considerably. (C) 2016 AIP Publishing LLC.