Pickering Emulsion

A Pickering emulsion is a type of emulsion that is stabilized by solid colloidal particles instead of traditional surfactants like soaps or detergents. The surfactants are typically low-molecular-weight and can be natural amphiphilic macromolecules. Pickering emulsions are commonly encountered in the food, cosmetic and pharmaceutical industries (Gao et al., 2021).

In a normal emulsion (like oil and water mixed with soap), surfactant molecules reduce the surface tension between the two liquids and help keep the droplets stable. In a Pickering emulsion, tiny solid particles — often silica, clay, or starch, for example — sit at the interface between the oil and water phases. These particles form a barrier around the droplets, preventing them from coalescing (merging back together). Their stability against coalescing is one of the key benefits of such a system.

From a physical chemistry perspective,, the desorption energy for removing adsorbed particles from a biphasic surface allows irreversible adsorption with a steric barrier at the oil-water interface.

Key features of Pickering emulsions:

• The solid particles must be partially wetted by both the oil and the water.

• They are often more stable than surfactant-based emulsions.

• They can be either oil-in-water (O/W) or water-in-oil (W/O) emulsions, depending on how the particles interact with each phase.

• They are used in foods, cosmetics, drug delivery, and even in some industrial processes. They’ve been used to protect probiotics, for encapsulation of various nutraceuticals, as a substitute for hydrogenated oils and saturated fatty acids amongst others.

Examples

(1) A milkshake stabilized by tiny cellulose particles instead of milk proteins could be considered a type of Pickering emulsion.

(2) Novel mayonnaises.

These types of emulsions can be manipulated to generate a particular appealing appearance with special rheological and stabilizing properties.

The Pickering emulsifiers include a variety of materials such as:-

• carbohydrate-based particles (e.g., modified starch particles, microcrystalline cellulose),
• protein-based particles (e.g., gluten, zein and soy protein particles),
• lipid-based particles (e.g., fat crystals).
• inorganic particles (e.g., silica and calcium carbonate particles).

References

Gao, H., Ma, L., Cheng, C., Liu, J., Liang, R., Zou, L., … & McClements, D. J. (2021). Review of recent advances in the preparation, properties, and applications of high internal phase emulsions. Trends in Food Science & Technology, 112, pp. 36-49.