miniemulsions

Miniemulsions are submicron emulsions in which the dispersed phase forms droplets typically in the range of about 50 to 500 nanometers. They are stabilized by surfactants, often in combination with co-stabilizers, and sometimes by solid particles, enabling kinetic stability at small droplet sizes. Miniemulsions can be oil-in-water or water-in-oil systems and are formed by high-energy methods such as high-pressure homogenization, ultrasonication, or rotor-stator emulsification. The small droplet size reduces the tendency for coalescence, but Ostwald ripening can still occur unless it is suppressed by using a lipophilic co-stabilizer (for example hexadecane) or by incorporating polymerizable monomers that can be cross-linked within droplets.

Stabilization typically relies on surfactants appropriate to the chosen oil and water phases, sometimes supplemented by polymers. In some approaches, particles are used at the interface to provide Pickering stabilization. The droplets are generally stabilized temporarily and may be processed further, for example by polymerization, to lock in the droplet size and form solid particles.

Miniemulsions have wide applications as templates for polymer latex particles via miniemulsion polymerization, enabling size-controlled polymers and nanocomposites. They are also used in cosmetics, pharmaceuticals, coatings, and food applications, either as delivery systems or carriers for encapsulated actives. Advantages include the ability to produce uniform, small droplets and compatibility with sensitive ingredients; limitations include the need for precise formulation, energy input, and storage- and process-stability considerations.