Description
An emulsion is a mixture of two or more liquids that are normally
immiscible (nonmixable or unblendable). Emulsions are part of a
more general class of two-phase systems of matter called colloids.
Although the terms colloid and emulsion are sometimes used
interchangeably, emulsion should be used when both the dispersed
and the continuous phase are liquids. In an emulsion, one liquid
(the dispersed phase) is dispersed in the other (the continuous
phase). Examples of emulsions include vinaigrettes, milk,
mayonnaise, and some cutting fluids for metal working. The
photo-sensitive side of photographic film is an example of a
colloid.
The word "emulsion" comes from the Latin word for "to milk", as
milk is (among other things) an emulsion of milk fat and water.
Two liquids can form different types of emulsions. As an example,
oil and water can form, firstly, an oil-in-water emulsion, where
the oil is the dispersed phase, and water is the dispersion medium.
Secondly, they can form a water-in-oil emulsion, where water is the
dispersed phase and oil is the external phase. Multiple emulsions
are also possible, including a "water-in-oil-in-water" emulsion and
an "oil-in-water-in-oil" emulsion.
Emulsions, being liquids, do not exhibit a static internal
structure. The droplets dispersed in the liquid matrix (called the
“dispersion medium”) are usually assumed to be statistically
distributed.
