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Water-in-oil-in-water emulsions, commonly abbreviated as W/O/W, are a class of multiple emulsions in which water droplets are dispersed within oil droplets that are themselves dispersed in a continuous water phase. These systems enable encapsulation of both hydrophilic and lipophilic agents and can provide protection, masking of tastes, and controlled release of active ingredients.

In these systems, the inner water phase (W1) is encapsulated by a lipophilic oil phase (O), which is then dispersed in an external aqueous phase (W2). Stabilization requires two interfacial layers, typically achieved with surfactants or polymers that selectively stabilize the W1/O and O/W2 interfaces. The design aims to protect the internal water from coalescence, enable encapsulation of active ingredients, and allow controlled release.

Production usually involves a two-step emulsification. A primary W1/O emulsion is prepared, then this emulsion is emulsified into the external aqueous phase to form W1/O/W2. Techniques include high-shear mixing, ultrasonication, and membrane emulsification; process parameters influence droplet size, stability, and encapsulation efficiency.

Stability and challenges: W/O/W emulsions are prone to coalescence, Ostwald ripening, diffusion of oil droplets, phase inversion, and leakage of the inner water phase under osmotic or ionic conditions. Selection of compatible surfactants or polymers and control of phase volumes, temperature, and osmolarity are crucial for robust formulations.

Applications: In pharmaceuticals, W/O/W emulsions are used for controlled release of hydrophilic drugs, protection of sensitive molecules, and masking of tastes. In cosmetics, they provide moisturization and staged delivery of active ingredients. In food and nutraceuticals, they enable encapsulation of flavors and nutrients.

Limitations: complex formulation, stability concerns, potential incompatibilities with ingredients, regulatory considerations, and higher production costs. Ongoing research seeks improved stability via novel stabilizers and production methods.