Mechanism of Micelle Formation

Definition of Micelles (Associated colloids)

There are some substances which at low concentrations behave as normal strong electrolytes but at higher concentrations exhibit colloidal behavior due to the formation of aggregated particles. These associated particles are called micelles or associated colloids. The formation of micelles take place only above a particular temperature called Kraft temperature (T_K) and above a particular concentration called critical micelle concentration (CMC).
Example: Detergents and soaps.



Soap is sodium salt of higher fatty acid like C₁₇H₃₅COONa (sodium stearate). In aqueous solution soap ionizes as The RCOO^- ions (C₁₇H₃₅COO^-) and Na⁺ ions.

C₁₇H₃₅COONa ---------> C₁₇H₃₅COO^- + Na⁺

The RCOO^- ions however consist of two parts. That is, long hydrocarbon chain R(-C₁₇H₃₅) also called non-polar tail which is hydrophobic and the polar group COO^- called polar-ionic head which is hydrophilic. In concentrated solution, these stearate ions get aggregated to form colloidal solution or micelles. For soaps the critical micelle concentration (CMC) is 10^-4 to 10^-3 mol Lsup>-


Related chemistry article Lyophilic colloids and lyophobic colloids