Classification based on types of particle of dispersed phase
Depending upon the type of the particles of the dispersed phase, the colloids are classified as follows.
(a) Multimolecular colloids
• When on dissolution, atoms or smaller molecules of substances (having diameter less than 1nm) aggregate together to form particles of colloidal dimensions, the particles thus formed are called multimolecular colloids.
• In these sols the dispersed phase consists of aggregates of atoms or molecules with molecular size less than 1 nm.
• For example, sols of gold atoms and sulphur molecules. In these colloids, the particles are held together by Vander Waal's forces. They have usually lyophilic character.
(b) Macromolecular colloids
• These are the substances having big size molecules (called macromolecules) which on dissolution form size in the colloidal range. Such substances are called macromolecular colloids.
• These macromolecules forming the dispersed phase are generally polymers having very high molecular masses.
• Naturally occurring macromolecules are starch, cellulose, proteins, enzymes, gelatin etc. Artificial macromolecules are synthetic polymers such as nylon, polythene, plastics, polystyrene etc.
• They have usually lyophobic character.
(c) Associated colloids
• These are the substances which on dissolved in a medium behave as normal electrolytes at low concentration but behave, as colloidal particles at higher concentration due to the formation of aggregated particles. The aggregates particles thus formed are called micelles.
• Their molecules contain both lyophilic and lyophobic groups.
• Micelles are the cluster or aggregated particles formed by association of colloid in solution.
• The common examples of micelles are soaps and detergents.
• The formation of micelles takes place above a particular temperature called Kraft temperature and above a particular concentration called critical micellization concentration (CMC).
• They are capable of forming ions.
• Micelles may contain as many as 100 molecules or more.
• For example sodium stearate is a typical example of such type of molecules.
• When sodium stearate is dissolved in water, it gives and ions.