Emulsion << ih MUHL shuhn >> is a colloid (mixture) of one liquid evenly dispersed in another liquid. The two liquids do not dissolve in each other. Rather, tiny drops of the dispersed liquid remain suspended in the other liquid. These drops range in size from about 0.1 to 20 micrometers. A micrometer equals 0.001 millimeter or 1/25,400 of an inch.
Some common substances such as cosmetic lotions, foods, lubricants, medicines, and paints are emulsions. Photographic film is coated with a light-sensitive colloid that is incorrectly called an emulsion.
Emulsions are not permanently stable. The liquids separate from each other after a certain time. To help keep them mixed, an emulsifying agent is needed.
Oil and water form the most common emulsions. An emulsion can be formed by either droplets of oil dispersed in water or droplets of water in oil. Milk is an emulsion of butterfat in water. The emulsifying agent that keeps butterfat suspended in milk is the protein casein.
See also Colloid; Photography (Exposing the film); Suspension.
