When some solid is dispersed into a medium in which the solid substance is otherwise insoluble such that after dispersion, the size of the colloidal particles lies in the colloidal range, the system is called a colloidal dispersion. Examples of colloidal dispersion are gold sol, a colloidal dispersion of as 2S3 in water etc.
Depending upon how the different substances may have size in the range of the colloids, the various types of colloids or colloidal dispersions may be divided into the following three categories:
Multimolecular colloids:
When on dissolution a large number of atoms or smaller molecules of a substance aggregate together to form species having size in the colloidal range, the species thus forms are multimolecular colloids. The dispersed phase in this type of colloidal system may contain large aggregates of atoms or molecules as a result of aggregating properties of the dispersing particles.
Macromolecular colloids:
When certain substances having big size molecules called macromolecules, having large molecular masses are dissolved in a suitable liquid, they form a solution in which the molecules of the substances i.e. the dispersed particles have size in the colloidal range. Such substances are called Macromolecular colloids.
These Macromolecular substances are usually polymers with very high molecular masses. Examples of naturally occurring Macromolecules are starch, cellulose, proteins, enzymes and gelatin.
Examples of manmade Macromolecules are polythene, nylon, polystyrene, synthetic rubber etc.
Associated colloids (Micelles):
The substances which when dissolved in a medium at low concentrations behave as normal, strong electrolytes but at higher concentrations exhibits colloidal state properties due to the formation of aggregate particles as called associated colloids.
