emulsionsnanoscale

Emulsions nanoscale, commonly called nanoemulsions, are emulsions in which the dispersed phase forms droplets with diameters typically in the range of 20 to 200 nanometers. They are dispersions of one immiscible liquid in another, stabilized by surface-active agents such as surfactants, polymers, or solid particles. Nanoemulsions are usually kinetically stable but thermodynamically unstable, meaning that droplets can coarsen or dissolve over time, albeit on extended time scales.

Types include oil-in-water and water-in-oil emulsions, depending on the continuous phase. Stabilization mechanisms include conventional surfactants forming an interfacial film, polymeric stabilizers increasing steric hindrance, and solid-particle coatings in Pickering nanoemulsions. The choice of stabilizer influences viscosity, Ostwald ripening rate, and biocompatibility, and can determine whether the system is more suitable for topical, oral, or injectable use.

Production methods are categorized as high-energy and low-energy. High-energy approaches use mechanical forces to break droplets, such as high-pressure homogenization, rotor-stator shearing, or ultrasonication. Low-energy methods rely on physicochemical conditions to drive self-assembly, including phase inversion temperature, spontaneous emulsification, or solvent displacement, often achieving narrow size distributions with reduced energy input.

Characterization techniques include dynamic light scattering for size distribution, zeta potential for surface charge, and electron microscopy (TEM or cryo-TEM) for morphology. Nanoparticle tracking analysis can provide concentration and size data, while rheology and interfacial tension measurements help assess stability and flow properties.

Nanoemulsions find applications in pharmaceuticals and drug delivery, cosmetics, food and flavors, and materials processing, where a high interfacial area and rapid diffusion can enhance solubility and bioavailability. Challenges include long-term stability against coalescence and Ostwald ripening, scalable production, and regulatory considerations for components.