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Abstract:
This communication presents a comprehensive investigation into the impact of mixing on the synthesis of water-in-water Pickering emulsions. The approach employs commercial-grade oppositely charged nanoparticles within two distinct fluid phases, facilitating self-assembly and the formation of aggregates with variable sizes and compositions. Enhanced interfacial area, achieved through aggregate adsorption at the interface, elevates the Gibbs detachment energy of particles between the two aqueous phases, leading to stable emulsion formation. We further explore the effect of various mixing devices, including high-pressure and sonic wave mixing. Our findings reveal that mixing within the aqueous phase critically influences emulsion size, with sonicator-assisted mixing producing smaller droplets than homogenizer mixing. Both devices yield poly-dispersed droplet size distributions. Interestingly, the droplet size correlates well with the Hinze scale (hd), and the Kolmogorov length scale (ld) exhibits good correspondence within a specific operating range. The proposed method introduces a streamlined, one-step synthesis process for easy preparation, demonstrating excellent stability for a minimum of 30 days. This study pioneers the investigation of mixing effects within an aqueous two-phase system utilizing a Pickering emulsion template.

Abstract:
This communication presents a simple yet straightforward method for preparing water-in-water-in-water particle-stabilized double emulsions, also known as Pickering double emulsions. The approach involves using oppositely charged nanoparticles (OCNPs) in two distinct fluid phases, promoting self-assembly and the formation of aggregates with varying sizes and compositions. By enhancing the interfacial area through the adsorption of aggregates at the interface, this method increases the Gibbs detachment energy of particles between the two aqueous phases, forming stable double emulsions. Furthermore, we investigated the impact of the molecular weight of polyethylene oxide and dextran in the respective fluid phases and the mass ratio (M) of the OCNPs on double emulsion formation. The results demonstrate that the molecular weight of the polymers used in the aqueous phase is a critical parameter influencing the structural formation of the emulsion and the generation of double emulsions. Consequently, double emulsions are formed when equal molecular weight polymer mixtures are employed at an appropriate M, with the dispersed phase placed in the highly viscous continuous phase. The proposed method offers a one-step synthesis process, enabling easy preparation, and exhibits excellent stability for at least 30 days. This study represents the first reported approach for the one-step synthesis of multiple emulsions in an aqueous two-phase system utilizing a Pickering emulsion template.

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