Osmotically Driven Formation of Double Emulsions Stabilized by Amphiphilic Block Copolymers

Double emulsions are valuable for the formation of multi‐compartmental structures. A variety of pathways to prepare double emulsions have been developed, but high‐throughput routes to droplets of controlled size and architecture remain scarce. A new single‐step process is introduced for preparation of water‐in‐oil‐in‐water double emulsions by a previously unexplained process of self‐emulsification. We show that the origin of this process is the osmotic stress resulting from the presence of salt impurities within the amphiphilic block copolymers used for emulsion stabilization. Further, we utilize osmotically driven emulsification to tailor the structures of multiple emulsions, which upon solvent evaporation can yield multi‐compartmental capsules or hierarchically structured porous films. Water‐in‐oil‐in‐water (w/o/w) double emulsions are spontaneously generated from o/w single emulsions by the osmotic pressure provided by salt species initially dispersed in the oil phase. This phenomenon provides a simple route to tailor block copolymer self‐assembly, yielding multi‐vesicular structures and hierarchically structured porous films after solvent evaporation.