Nanoemulsions

Nanoemulsions are emulsions with droplet diameters in the nanometer range, typically from about 20 to 200 nanometers. They can be oil-in-water or water-in-oil systems, with a continuous aqueous or oil phase, respectively. Nanoemulsions are stabilized by surfactants, often with co-surfactants, to form kinetically stable dispersions. They are typically thermodynamically unstable but resistant to separation due to the small droplet size and interfacial film.

Formulation components include an oil phase (which may dissolve lipophilic active ingredients), an aqueous phase, a surfactant, and sometimes a co-surfactant or cosolvent. The choice depends on the intended application and the solubility of the active ingredient. Methods to prepare nanoemulsions are divided into high-energy approaches, such as high-pressure homogenization and ultrasonic emulsification, and low-energy approaches, such as phase inversion temperature or spontaneous emulsification. The resulting droplets have narrow size distributions and low turbidity, with stability influenced by interfacial film strength.

Applications cover pharmaceuticals (enhanced solubility, bioavailability, topical and oral delivery), cosmetics and personal care (lightweight, transparent emulsions), nutraceuticals and food (flavor and nutrient delivery), and agrochemicals. Nanoemulsions can enable controlled release and improved taste masking, masking of bitterness, and targeted delivery in some systems.

Stability considerations include Ostwald ripening as a common mechanism of destabilization, coalescence, and phase separation. Stability is improved by selecting appropriate oil and surfactant systems and optimizing the surfactant-to-oil ratio; storage conditions such as temperature and pH also matter. Safety concerns partly relate to surfactant toxicity and regulatory status, particularly for oral or dermal applications.