We have classified colloids on the basis of the dispersed phase and the dispersion medium into categories such as solid sol, sol, aerosol, emulsion, gel, foam etc. and also in the basis of the nature of the interaction between the dispersion medium and the dispersed phase into lyophilic and lyophobic colloids. In this section, we will choose another basis of classification of the colloids, that is, the type of particles of the dispersed phase.
On the basis of the types of particles in the dispersed phase, colloids can be classified into the following types:
- Multimolecular colloids
- Macromolecular colloids
- Associated colloids
Multimolecular colloids: When the dissolution of smaller molecules of a substance or a large number of atoms takes place, they combine to form a species whose size is in the range of colloidal size. The species formed is known as the multimolecular colloid.
For example, Sulphur solution contains particles which have thousands of S8 molecules.
Macromolecular colloids: In this type of colloids, the macromolecules from a solution with a suitable solvent. The size of the particles in the macromolecular solution lies in the range of colloidal particle size. Thus this solution is also known as the macromolecular colloid. The colloid formed here is similar to that of the actual solution in many respects and are very stable.
Example: Starch, proteins, enzymes, and cellulose are the naturally occurring macromolecular colloids whereas polyethylene, synthetic rubber, etc. are the synthetic macromolecules.
Associated colloids: Some substances act as strong electrolyte when they are in low concentrations, but they act as colloidal solutions when they are in high concentration. In higher concentration, particles aggregate showing a colloidal behavior. These aggregated particles are known as the micelles. They are also known as the associated colloids. The formation of the micelles occurs above a particular temperature called the Kraft temperature (Tk) and also above a specific concentration called the critical micelle concentration. These colloids can be reverted by diluting them.
Examples of some associated colloids are soaps and synthetic detergents.
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