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Critical Micelle Concentration. uuuuuuuuu water. Micelles : They are aggregates of SAA molecules formed in the bulk of the liquid after the surface became saturated with SAA molecules..

Surfactant Type Polar head charge Example Anionic - ve Charge Sodium lauryl sulphate Cationic + ve Charge Cetrimide Non-ionic None Span Tween Ampholytic (Amphoteric) ( Zwitterionic ) Depend upon solution pH Dodecyl alanine.

Factors affecting c.m.c of SAA. Structure of the hydrophobic group.

1- Structure of the hydrophobic group. The driving mechanism for micellization is the transfer of hydrocarbon chains from water into the oil-like interior. This entropic effect is called hydrophobic effect..

. 2- Nature of the hydrophilic group. In general, nonionic surfactants have very much lower c.m.c values than their ionic counterparts with similar hydrocarbon chains, mainly because the micellisation process for such compounds does not involve any electrical work..

3- Addition of electrolytes. Addition of electrolytes to ionic surfactants decreases the cmc . The effect is simply explained in terms of a reduction in the magnitude of the forces of repulsion between the charged head groups in the micelle and a consequent decrease in the electrical work of micellisation ..

Alcohol effect on c.m.c. Addition of alcohol to water decrease micelle electrical potential so micelles will be formed at lower SAA concentration..