Emulsion - Emulsifier

An emulsion is a mixture of two or more immiscible (unblendable) liquids.

Emulsions are mainly used in many major chemical industries. In the pharmaceutical industry, they are used to make medicines that are more tasty, to improve value by controlling the amount of active ingredients. The most popular emulsions are Non-ionic because they have low toxicity. Cationic emulsions are also used in some products because their antimicrobial properties. Antimicrobial is a substance that kills or avoids the growth of microorganisms such as fungi and bacteria. Emulsions are also used in the making many hair and skin products such as of various types of oils and waxes.

An emulsifier (also known as an emulgent) is a substance which stabilizes an emulsion by increasing its kinetic stability. One class of emulsifiers is known as surface active substances, or surfactants. Examples of food emulsifiers are egg yolk (where the main emulsifying agent is lecithin), honey, and mustard, where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers; proteins and low-molecular weight emulsifiers are common as well. Soy lecithin is another emulsifier and thickener. In some cases, particles can stabilize emulsions as well through a mechanism called pickering stabilization. Both mayonnaise and Hollandaise sauce are oil-in-water emulsions that are stabilized with egg yolk lecithin or other types of food additives such as Sodium stearoyl lactylate.
Detergents are another class of surfactant, and will physically interact with both oil and water, thus stabilizing the interface between oil or water droplets in suspension. This principle is exploited in soap to remove grease for the purpose of cleaning. A wide variety of emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions. Common examples include emulsifying wax,cetearyl alcohol,polysorbate 20, , and ceteareth 20. Sometimes the inner phase itself can act as an emulsifier, and the result is nanoemulsion - the inner state disperses into nano-size droplets within the outer phase. A well-known example of this phenomenon, the ouzo effect, happens when water is poured in a strong alcoholic anise-based beverage, such as ouzo, pastis, arak or raki. The anisolic compounds, which are soluble in athanol, now form nano-sized droplets and emulgate within the water. The colour of such diluted drink is opaque and milky.

Oil-in-water emulsions are common in food. Notable examples include:
•Vinaigrette – vegetable oil in vinegar; if prepared with only oil and vinegar (without an emulsifier), yields an unstable emulsion
•Mayonnaise – vegetable oil in lemon juice or vinegar, with egg yolk lecithin as emulsifier
•Hollandaise sauce – similar to mayonnaise
•Crema in espresso – coffee oil in water (brewed coffee), unstable

In pharmaceutics, hairstyling, personal hygiene and cosmetics, emulsions are frequently used. These are usually oil and water emulsions, but which is dispersed and which is continuous depends on the pharmaceutical formulation. These emulsions may be called creams, ointments, liniments (balms), pastes, films or liquids, depending mostly on their oil and water proportions and their route of administration. The first 5 are topical dosage forms, and may be used on the surface of the skin, transdermally, ophthalmically, rectally or vaginally. A very liquidy emulsion may also be used orally, or it may be injected using various routes (typically intravenously or intramuscularly). Popular medicated emulsions include calamine lotion, cod liver oil, Polysporin, cortisol cream, Canesten and Fleet.