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Emulsions - Lesson Summary

Emulsions are liquid-liquid colloidal systems in which both, the dispersed phases as well as the dispersion medium are liquids.

An emulsion may be defined as a colloidal dispersion of two immiscible or partially immiscible liquids, in which one liquid acts as the dispersion medium and the other as the dispersed phase.

Depending on the nature of the dispersed phase, emulsions are broadly classified into two types

They are

Oil in water type emulsions:

In this type of emulsions, oil acts as the dispersed phase and water acts as the dispersion medium.

EX: Milk is an emulsion of liquid fat globules dispersed in water.

Water in oil type of emulsions:

Water acts the dispersed phase and oil acts as the dispersion medium.

EX: Butter is an emulsion of water dispersed in fat.

Emulsions are generally unstable and separate in two layers on standing.

Thus, to stabilise an emulsion, small quantities of certain other substances, called emulsifiers or emulsifying agents, are added.

Proteins, gums, natural and synthetic soaps, detergents, etc. are the principal emulsifying agents for oil in water type of emulsions.

Heavy metal salts of fatty acids, long chain alcohols, lamp black, etc. are used for water in oil type of emulsions.

Emulsions exhibit properties like the Tyndall effect, the Brownian movement, electrophoresis, coagulation or de-emulsification on the addition of electrolytes etc…

An emulsion can be separated into its constituent liquids by boiling, freezing, centrifuging, electrostatic precipitation, etc.

EX: Centrifuging is the separation of cream from milk.

Application of emulsions:

Large number pharmaceuticals in the form of lotions, creams and ointments, which are oil in water or water in oil type of emulsions.

The cleansing action of soap is based upon the formation of an 'oil in water' emulsion.

The concentration of ore by the froth floatation process is based upon the treatment of the powdered ore with an oil emulsion.

Milk, is an emulsion of liquid fat droplets in water.

The digestion of fats in our body takes place by the process of emulsification.

Asphalt emulsified in water is used for building roads without the necessity of melting the asphalt.


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