Emulsion

A very fine, stable suspension of two insoluble liquids

Water and oil repel each other and do not mix. Emulsifiers are compounds that enable oil and water to form a stable, fine suspension.

A common example of an emulsion is mayonnaise, which consists of egg yolk, vinegar and oil. The oil and water (vinegar) do not mix, but the presence of lecithin, contained in the egg yolk, prevents the oil and water from separating into layers. Emulsifiers are very important for the food industry. Some of the most important emulsifiers include salts of higher fatty acids, fatty alcohols, gelatin, polysaccharides and casein.
Household detergents work by forming emulsions, enabling greasy dishes to be cleaned with water. The detergent can mix with grease, but can also be rinsed off with water.