Spray-assisted formation of micrometer-sized emulsions

Emulsion drops with defined sizes are frequently used to conduct chemical reactions on picoliter scales or as templates to form microparticles. Despite tremendous progress that has been achieved in the production of emulsions, the controlled formation of drops with sizes of a few µm at high throughputs remains challenging. Drops of this size, however, are in high demand for example for many pharmaceutical, food, and material science applications. Here we introduce a scalable method to produce water-in-oil emulsion drops possessing controlled diameters of just a few microns: We fabricate calibrated aerosol drops and transfer them into an oil bath to form stable emulsions at rates up to 480 µl min-1 of the dispersed phase. We demonstrate that the emulsification is thermodynamically driven such that design principles to successfully form emulsions can easily be deduced. We employ these emulsion drops as templates to form well-defined µm-sized hydrogel spheres and capsules.