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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 C 17 H 35 COONa (sodium stearate). In aqueous solution soap ionizes as The RCOO - ions (C 17 H 35 COO - ) and Na + ions. C 17 H 35 COONa ---------> C 17 H 35 COO - + Na + The RCOO - ions however consist of two parts. That is, long hydrocarbon chain R(-C 17 H 35 ) also called non-polar tail which is hydrophobic and the polar group COO - called polar-ionic head which is hydrophilic. In concentrated solution,...

Depending upon the nature of interaction between the dispersed phase and the dispersion medium, colloids are classified in to the lyophilic colloids (solvent attracting) and lyophobic colloids (solvent repelling). If water is the dispersion medium, it is called as hydrophilic and hydrophobic colloid respectively. Lyophilic colloids The meaning of the word 'lyophilic' is 'liquid-loving' or 'solvent attracting'. That means, these are colloids in which there is strong interaction between the two phases. Lyophilic colloids are those dispersions in which the dispersed phase exhibits a definite affinity for the medium and as a results extensive solvation of the colloidal particles takes place. They are directly formed by mixing the two phases.Eg :- Gum, soap, starch, gelatin, rubber etc. These sols are also called reversible sols. Because, if the dispersion medium is separated from the dispersed phase, the sol can be reconstituted by simply mixing with the dispersion...