Pickering emulsion

Pickering Emulsion

A Pickering emulsion is a type of emulsion that is stabilized by solid particles which adsorb onto the interface between the two phases. Named after British chemist Spencer Umfreville Pickering, who first described this phenomenon in 1907, Pickering emulsions have been extensively studied and utilized in various fields, including food science, cosmetics, pharmaceuticals, and petroleum recovery.

Overview

Unlike traditional emulsions that are stabilized by surfactants, Pickering emulsions are stabilized by solid particles. These particles can be inorganic, organic, or even biological in nature. The particles attach to the oil-water interface, creating a barrier that prevents the droplets from coalescing. This results in a more stable emulsion, with droplets that can remain separate for extended periods of time.

Mechanism

The stability of a Pickering emulsion is determined by the wettability of the particles. This is typically quantified by the contact angle, θ, which is the angle at which a liquid/vapor interface meets a solid surface. Particles with a contact angle of 0° completely wet the surface and are not suitable for stabilizing emulsions. Particles with a contact angle of 180° do not wet the surface at all and are also unsuitable. Particles with a contact angle between these two extremes can stabilize emulsions, with the most stable emulsions being formed by particles with a contact angle close to 90°.

Applications

Pickering emulsions have a wide range of applications. In the food industry, they are used to create stable, low-fat spreads and dressings. In cosmetics, they are used to create creams and lotions with a smooth texture and long shelf life. In pharmaceuticals, they are used to deliver drugs in a controlled manner. In petroleum recovery, they are used to enhance the recovery of oil from reservoirs.

See also

• Emulsion
• Surfactant
• Wettability
• Spencer Umfreville Pickering