5. Emulsions

EMULSIONS 

Pair of immiscible liquid is called emulsion. Emulsion are unstable and some time they are separated into two layers on keeping still, for the stabilising of an emulsion, a third  component is added called emulsifying-Agent form an interfacial film between D.P. and D.M.

Emulsion droplets are bigger than sol particles and can be seen under an ordinary microscope and sometimes even with a magnifying glass.

Example : Milk is an emulsion in which liquid fat is D.P. and liquid water is D.M. and casein is emulsifying agent.

Demulsification :  The separation of an emulsion into its constituent liquids is called demulsification. Various techniques employed for this are freezing, boiling, centrifugation, electrostatic precipitation or chemical methods which destroys the emulsifying agents.

Demulsification can be brought about by :

(i)  Freezing

(ii)  Heating

(iii) Centrifugal action (Separation of cream of milk done by centrifugation).

(iv) Removal of emulsifiers by adding a better solvent for them like alcohol, phenol etc, called demulsifiers.

Types of emulsions : Depending on the nature of the dispersed phase, the emulsions are classified as :

(a) Oil in water emulsions

(b) Water in oil emulsions

(a)  Oil in water emulsions (o/w) : This type of emulsions is formed when oil D.P. and water D.M.

Ex. :- Milk and vanishing cream are oil - in - water type emulsions.

(b)  Water  in oil emulsions (w/o) : This type of emulsions is formed when water is D.P. and oil is D.M.

Ex. : - Cold cream and cod liver oil.

[B] Applications of emulsions :

Disinfactants like phenyl, dettol when mixed with water form emulsion.

Digestion of fat in small intestine occurs easily due to emulsion.

In metallurgical process the concentration of ore by froath floatation method is based upon emulsion.

Milk is an emulsion of liquid fat in water in which casein emulsifying agent.

Cleansing action of soap is due to formation of emulsions. Soaps and detergents emulsify the grease along with the adhering dirt and carry them away in the wash water.

For concentrating ores, the finely powdered ore is treated with an oil. Oil forms emulsion with the ore particles. When air is bubbled into the mixture, emulsion containing the particles of the mineral are carried to the surface.