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Abstract:
Nanoparticle-stabilized water-in-water (w/w) emulsions, an example of aqueous two-phase systems (ATPS), can produce low-fat food colloids, edible gels, bio-polymer-based bijels, scaffolds for tissue-engineering, and porous materials. This w/w emulsion is made from two thermodynamically incompatible aqueous-polymer solutions, such as polyethylene oxide (PEO) and dextran. Changing the molecular weight of PEO in one aqueous phase stabilizes w/w emulsion. The state diagram we generated using electron and light microscopy provides a novel approach to producing stable emulsion-filled gels and emulsion droplets. The visual examination, brightfield, and fluorescent microscopy studies highlight the role of molecular weight and storage duration. The production of an emulsion-filled gel is ascribed to the “active-filler-particles” arrangement, typically seen when the affinity between droplets stabilized by particles and polymer is substantial. In contrast, we expect the “inactive-filler-particles” arrangement for the samples that undergo phase inversion. The temporal evolution of shear-induced structures recorded using a rheometer demonstrates that these emulsion-filled gels’ viscoelastic properties correspond directly with time, molecular weight, and polymer composition. The emulsion-filled gels generated displayed 90-day storage stability. Our work would help us understand the complex dynamics of w/w emulsion-based formulations that need suitable size, shape, appearance, and shelf life management.

Keywords:
W/W emulsions, ATPS, Emulsion-filled gels, Rheology, Silica nanoparticles