Nanoemulsion

Nanoemulsions are emulsions with droplet sizes in the nanometer range, typically 20 to 200 nanometers. They are oil-in-water (O/W) or water-in-oil (W/O) dispersions stabilized by surfactants, often with cosurfactants. Unlike microemulsions, nanoemulsions are not thermodynamically stable and require energy input or specific formulations to form and remain dispersed.

Production methods are categorized as high-energy and low-energy. High-energy techniques include high-pressure homogenization and ultrasonication, which break droplets to nanoscale sizes. Low-energy approaches rely on formulation changes, such as phase inversion temperature, to generate nanosized droplets with milder processing conditions.

The small droplet size yields a clear to translucent appearance and a high interfacial area, which can improve the solubility and bioavailability of poorly water-soluble compounds. Nanoemulsions can enable controlled release and protection of active ingredients, but are prone to physical instabilities such as Ostwald ripening and coalescence if stabilizers are insufficient. Stability depends on the interfacial film created by surfactants and co-surfactants, as well as the overall formulation.

Applications span pharmaceuticals, nutraceuticals, cosmetics, foods, and agrochemicals. They are used to improve oral, topical, or injectable delivery of lipophilic drugs, to formulate transparent cosmetic products, and to distribute flavors or fragrances. Safety and regulatory considerations focus on surfactant toxicity, oil choice, and formulation compatibility.

Characterization typically involves droplet size analysis by dynamic light scattering, zeta potential measurements, and imaging by electron microscopy. Stability testing, rheology assessment, and in vitro release studies are standard components of development.