Emulsion

The resulting emulsion has physical properties different from either of its two components. For example, while water and oils are transparent, emulsions are usually opaque and may be designed to have a lustrous, pearlized appearance. While water and oil are thin free flowing liquids, emulsions can be made as thick creams which do not flow. Furthermore, the tactile and spreading properties of emulsions are different than the materials of which they are composed.

One of the most important characteristics of emulsions is their inherent instability. Even though the dispersed drops are small, gravity exerts a measurable force on them and over time they coalesce to form larger drops which tend to either settle to the bottom or rise to the top of the mixture. This process ultimately causes the internal and external phases to separate into the two original components. Depending on how the emulsion is formulated and the physical environment to which it is exposed, this separation may take minutes, months, or millennia.