Stabilizing an all-aqueous two-phase system using oil-in-water droplets to mimic double emulsions

The production of water-in-water emulsion droplets, the coalescence of which is prevented by adding oil-in-water micrometric droplets is reported. Hexadecane (O) and cetyl trimethyl ammonium bromide (CTAB) were added to a W/W emulsion made of dextran (Dex)-enriched droplets in a Polyethyleglycol (PEG)-enriched continuous phase and the mixture was further sonicated. Using Nile red to label the oil droplets afforded to observe their presence at the surface of Dex droplets (5 µm) allowing stabilizing them, preventing coalescence of the W/W emulsion, and mimicking W/O/W double emulsions. Addition of sulfate derivative of Dextran (DexSulf) allowed stable droplets of slightly larger diameter. By contrast, addition of carboxymethyl Dextran (CMDex) destabilized the initial aqueous double-like emulsion, yielding sequestration of the oil droplets within the Dex-rich phase. Interestingly, addition of DexSulf to that unstable emulsion re-yielded stable droplets. Similar findings (destabilization) were obtained when adding sodium dodecyl sulfate (SDS) to the initial double-like emulsion, which reformed stable droplets when adding positively charged Dextran (DEAEDex) derivative. The use of fluorescently (FITC) labelled derivatives of Dextran (Dex, CMDex, DEAEDex and DexSulf) allowed to follow their position within, out or at the interface of droplets in the above-mentioned mixtures. These findings are expected to be of interest in the field of materials chemistry.