Effect of Alkyl Chain Stiffness and Branching on the Properties of Micelles Formed from 1-Methyl-4-(C12-alkyl)pyridinium Iodide Surfactants

Article abstract of DOI:10.1021/jo00246a006

This paper describes a study of the micellization of four 1-methyl-4-(C₁₂-alkyl)pyridinium iodide surfactants in which C₁₂-alkyl is n-dodecyl (1), 9,9-dimethyldecyl (2), 1-methylundecyl (3), and 1-dodec-5-ynyl (4).Alkyl chain branching (1-3) exerts only a minor effect on the stability of the micelles (as indicated by the cmc's) and on the properties of the micellar surface (as indicated by counterion binding, charge-transfer absorption bands, and kinetic data for decarboxylation of micellar-bound 6-nitrobenzisoxazole-3-carboxylate).By contrast, chain packing is substantially affected as revealed by large differences in the surfactant concentration (second cmc) for transition of spherical into rodlike micelles.The latter effects are rationalized in terms of the packing parameter P, introduced by Israelachvili.The alkyl chain in surfactant 4 is more stiff and somewhat less hydrophobic, leading to a higher cmc and modified behavior of the micelles toward the kinetic probe.