An emulsion is a type of胶体where both dispersed and continuous phases are immiscible liquids. Constant agitation or stirring keeps the emulsion mixed properly. However, if the emulsion is left for a period, both phases tend to separate (Figure 1).

Figure 1. Non-stable emulsions.A) Two immiscible liquids not emulsified yet; B) Emulsion of liquid 1 dispersed in liquid 2; C) Unstable emulsion separated.

乳剂are normally formed by a hydrophilic and a lipophilic substance and are extensively present in daily life. They can be found mainly in cosmetics, such as hair conditioners or sunscreens, and foods. Some examples of emulsions in food are mayonnaise (oil-in-water), vinaigrettes (water-in-oil), milk (oil-in-water), or margarine (water-in-oil).

Since emulsions are not stableper se, the addition ofemulsifiersis a common practice to stabilize them.