Associated colloids:
These are certain substance which when dissolved in a medium behave as normal electrolytes at low concentration but exhibit colloidal properties at higher concentration due to the formation of aggregated particles. These aggregated particles are known as micelles and dispersion of such substances are called associated colloids. e.g. Surface active agents like soap and synthetic detergent.
The minimum concentration required to form micelles is called Critical Micellisation Concentration (CMC) and its value depend upon the nature of dispersed phase. For soap CMC is 10-3 mole/litre. For example, in aqueous solution soap (sodium stearate) ionises as –
C17H35COONa ———–> C17H35C00– + Na+
Sod. Stearate Stearate ion
(soap)
Fig: Aggregation of C17H35C00– ions to form micelles