The definition of emulsion continued since 1930’s. According to International Union of Pure and Applied Chemistry (IUPAC), emulsion is stated as “In an emulsion, liquid droplets and/or liquid crystals are dispersed in a liquid”. The term emulsion was derived from the word emulgeo (meaning “to milk”). Milk is the best example for natural emulsion.
Emulsions could be water-in-oil (W/O), oil-in-water (O/W) and oil-in-oil (O/O) type. Emulsifier acts as a third component playing an important role in dispersing these two immiscible liquids (dispersed phase and continuous phase). The sizes of globules formed are of 0.25- 25 micrometers in diameter. Emulsions, the heterogenous system are classified based on the nature of emulsifier used and structure of the system formed. Microemulsions, nanoemulsions, microemulsions or micellar emulsions, mixed emulsions, double and multiple emulsions are the various structures of the system. The major critical factor concerning emulsion is their breakdown processes.