PickeringEmulsion

A Pickering emulsion, or particle-stabilized emulsion, is an emulsion in which solid particles adsorb at the oil–water interface to form a protective interfacial layer. This layer creates a mechanical barrier to droplet coalescence, making the droplets remain dispersed even in the absence of conventional surfactants. The stabilization arises from the energy required to remove a particle from the interface, which can be substantial for suitably wetted particles.

Stabilization depends on particle properties, especially wettability, size, and concentration. The phase that becomes continuous (oil-in-water or water-in-oil) is dictated by the particle’s contact angle with the phases: more hydrophilic particles tend to stabilize oil-in-water emulsions, while more hydrophobic particles favor water-in-oil emulsions. The droplets benefit from enhanced resistance to coalescence and often to Ostwald ripening, provided the particle coverage is sufficient. Particles are typically solid, partially wetted, and do not dissolve in the dispersed or continuous phase.

Common stabilizers include silica, clays, metal oxides, and various polymer or biopolymer particles; many are chosen for biocompatibility or food safety in relevant applications. Emulsions are usually prepared by dispersing one liquid phase into another under mechanical agitation in the presence of the particle suspension, with particle concentration carefully controlled to achieve the desired interfacial coverage.

History and naming: the phenomenon was described in the early 20th century by Ramsden and later by S. U. Pickering; the term “Pickering emulsion” honors Pickering. Applications span food, cosmetics, pharmaceuticals, catalysis, and materials science, where robust, surfactant-free stabilization is advantageous. Limitations include sensitivity to particle properties and potential desorption under extreme conditions.