Emulsion is a colloidal system in which both the dispersed phase and the dispersion medium are immiscible liquids e. g. milk, vanishing cream, butter etc.
Generally two types of the emulsions are recognized.
(i) Oil in water emulsion (o/w type) (Aqueous emulsion): In this, oil particles (dispersed phase) are distributed in water (dispersion medium) e.g. when a little nitrobenzene is distributed in large excess of water an emulsion of oil in water is formed. Other examples are milk, vanishing cream etc.
(ii) Water in oil emulsion (w/o type) (Oily emulsion): In this, water particles (dispersed phase) are distributed in oily liquid (dispersion medium) e.g. When a little water is shaken with large excess of nitro-benzene, an emulsion of water in oil is formed. Other examples are butter, cold creams etc.
The emulsion, so obtained, is not stable. In order to stabilise the emulsion, a third substance known as emulsiefier or emulsifying agent is added.
Soap, gelatin, gum arabic etc. are good emulsifiers. These emulsifiers form a thin film around every drop of the dispersed phase and thus prevent them from coming together.
Detection of Emulsions:
Following tests are used for it.
- Dye Test: o/w type emulsion is colourless with an oil soluble dye while w/ 0 gives colour.
- Electrical conductivity: o/w > w/o
- Viscosity test: w/o > o/w
- Dilution Test: 0/ w type of emulsion is easily diluted by water while for w/ o it is not possible.
Emulsions are of great technical importance in oil and fat, rubbre, paints and varnishes, adhesives, plastics, cellulose, paper, fiber and leather industries. They are also employed in medicines and are more effective than the oil as such e.g. emulsion of cod liver oil, shark liver oil etc., cleaning action of soap and detergent is due to emulsification of dirt etc. froth with ore is also emulsion.
Gel: Here dispersed phase is of liquid while dispersion medium is of solid.
E.g. Solid medium is generally gelatin Silicic acid, Sodium oleate etc. Formation of Gel is called Gelati-on.
Substance Cool it to get a semi solid gel
Non – Elastic Gel: By chemical methods like silica gel is prepared by the reaction of sodium silicate and HCl.
- On keeping gel for some time they get shrunk. It is called weeping of gel or Syneresis. While reversible sol-gel transformation is termed as Thixotropy.
- Elastic gel on keeping in water imbibe or get swell. These are reversible in nature e.g. Agar agar, gelatin, starch
- Non-elastic gels are irreversible and do not show inhibition e.g. silicic acid.
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