Emulsion:
Emulsion is the mixture of two immiscible liquids like oil
and water where mechanical energy is used to break up one component of the
mixture into small droplet that are dispersed in the other component with the
help of a surface active emulsifier to bring about stability. The most well
known emulsion is milk, which liquid will be dispersed in the other is
determined by two factors:
i.
The nature of the emulsifier(mainly its HLB
value)
ii.
Ratio of volume of two immiscible liquids
Thus an emulsion has two distinct phases – disperse phase
and outer continuous phase.
Emulsion in which oil is dispersed in water are described as
oil-in-water (o/w) emulsion whilst those in which water forms the disperse
phase are water-in-oil (w/o) emulsions.
Where disperse phase forms 70% of total volume, the emulsion
will have significant viscosity. Thus in a oil-in-water emulsion there is more
than 70% of total volume and in a water-in-oil emulsion there is more than 70%
of the total volume.
Here is an example of water-in-oil emulsion:
Oil------74%
Water-----25%
Emulsion---1%
Total---- 100%
As emulsifier we use detergent, soap and other surface
active agent.
The particle size of an emulsion is greater than 0.1μm since otherwise a
colloidal or true solution would exist. A distinction is made between macro and
micro emulsion according to their particle size and optical appearance.