Factors affecting the critical micelle concentration and micellar size

4 Factors affecting the critical micelle concentration and micellar size 

The hydrophobic group plays an important role in determining the type of association of the amphiphile. Compounds with rigid aromatic or heteroaromatic ring stmctures (many dyes, purines and pyrimidines, for example) associate by a nonmicellar process involving the face-to-face stacking of molecules one on top of the other, rather than by micellisation. Such systems do not exhibit cmcs. Association 

Many dmgs are surface active and form small micelles in aqueous solution. For these and other amphiphiles with more complex hydrophobic regions, the effect of substituents on hydrophobicity can be roughly estimated from Table 5.4 (section 5.2.1). in the series of micellar diphenylmethane dmgs shown in Table 6.3 there is an increased hydrophobicity (as evidenced by a decrease in cmc and increase in aggregation number) following the introduction of —CHj, —Br and —Cl substituents to the hydrophobic ring systems. 

The most important point to be noted here is the pronounced difference in properties between amphiphiles with ionic hydrophilic groups and those in which this group is uncharged, in general, nonionic surfactants have very much lower cmc values and higher aggregation numbers than their ionic counterparts with similar hydrocarbon chains, mainly because the micellisation process for such compounds does not involve any electrical work. 

The properties of the polyoxyethylated nonionic surfactants show a pronounced dependence on the length of the polyoxyethylene chain. An increase in the chain length confers 

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