Droplet Microfluidics with a Nanoemulsion Continuous Phase: Application in Reaction System Design for Material Synthesis

Recently, nanoemulsions have been incorporated into the dispersed phase in droplet microfluidics for the synthesis of hierarchical structured materials in which the different length scales between the nano-droplets and micro-droplets are exploited. In this study, we present a novel, generalizable method that uses a nanoemulsion as the continuous phase to generate uniform micro-droplets. The micro-droplets act as well-mixed micro-reactors/reservoirs with walls that are ‘permeable’ to the surrounding nanodroplets, with versatile control of ‘permeability’ by chemical, thermal, and electrical forces. The droplet generation physics and mass transfer processes between the micro- and nano-droplets are studied. Finally, we demonstrate the applications of this system in material synthesis for gel micro-beads, drug crystals, and nanoparticles. Our work expands the toolbox of droplet-based microfluidics, enabling new opportunities and applications involving active colloidal continuous phases carrying chemical payloads.