Colloids

Colloids are micro-heterogeneous dispersed systems, in which the size of the dispersed phase particles is within the range 1 - 1000 nm (4*10^-8 - 4*10^-5 inch).

The colloids phases (dispersion medium and dispersed phase) can not be separated under gravity, centrifugal or other forces.
Dispersed phase of colloids may be separated from the dispersion medium by micro-filtration.

Colloids are characterized by Tyndell effect - light is scattered when passing a colloid due to the similar dimensions of the light wavelength and the sizes of the colloidal dispersed particles.
Tyndell effect allows to differentiate colloids from Molecular dispersion (true solutions} and Coarse dispersions (suspensions) having dispersed particles either much smaller or much larger than the light wavelength.

Total interface area of the colloidal dispersed particles is very large due to their submicroscopic size.
The huge area-to-volume ratio determines specific properties and behavior of colloids.

Adsorption processes occurring on the interface between the dispersed and continuous phases exert considerable effect on the colloid physical properties, chemical reactions in the system and its stability.

Surface active substances added to a colloid modify its properties.
Classification of colloids:

	Dispersed phase
Continuous phase	Solid	Liquid	Gas
Solid	solid sol	solid emulsion	solid foam
Liquid	sol, gel	emulsion	foam
Gas	smoke	aerosol	-

The examples of colloids:

• Sols
  • Toothpaste
  • Starch solution
  • Silver iodide (AgI) in water
  • Clay sols
• Gels - sols, in which the dispersed particles are cross-linked forming a network. The properties of gels are similar to those of solid.
  • Jelly
  • Hair gel
  • Aloe Vera gel
  • Silica aerogel monolith
  • Alumina aerogel monolith
• Solid sols
  • Black diamond
  • Pigmented Polymers
  • Ruby glass
• Emulsions
  • Milk
  • Metal working fluids
  • Mayonnaise
• Solid emulsions
  • Butter
  • Opal
  • Pearl
• Liquid aerosols
  • Sprays
  • Fog
  • Smog
• Solid aerosols
  • Smoke
  • Fine dust in air
• Liquid foams
  • Whipped cream
  • Fire extinguisher foam
  • Meringues
• Solid foams
  • Charcoal
  • Expanded polystyrene
  • Lava
  • Pumice