The Micellar Properties of Ionic Surfactants Consisting of the α,ω-Type Surfactant Ion and the Same Type Counter Ion

Article abstract of DOI:10.1246/bcsj.70.761

The micellar properties of N, N, N, N', N', N'-hexamethyl-1, 20-icosanediyldiammonium, or the corresponding di(1-pyridinium)alkanedioates ^-OOC(CH₂)_nCOO^- (n = 2 - 10), were studied by conductivity and pyrene fluorescence measurements. In both systems, the critical micelle concentration (cmc) varied little up to n = 4, but decreased rapidly with a further increase in n. The binding degree (β) of the alkanedioate counter ion was virtually independent of the type of surfactant ion head group and gradually increased from 0.69 at n = 2 to 0.91 at n= 10. The observed n dependences of cmc and β were similar to those of the conventional ionic surfactants with an α,ω-type counter ion, indicating the importance of the hydrophobic interaction between the hydrocarbon part of the counter ion and the micellar core. On the basis of a phase-separation model, the transfer free energy per methylene group of the counter ion from aqueous-to-micellar environments was estimated to be about - 1.0 RT. The fluorescence measurements suggest that the surface layer of the micelle becomes progressively loose as n decreases. The micelle aggregation numbers of the bis (trimethylammonium) salts are of the order of 50.