NMR study of the transformation of perfluorinated surfactant solutions

Citation
H. Iijima et al., NMR study of the transformation of perfluorinated surfactant solutions, B CHEM S J, 72(2), 1999, pp. 171-177
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN
ISSN journal
0009-2673 → ACNP
Volume
72
Issue
2
Year of publication
1999
Pages
171 - 177
Database
ISI
SICI code
0009-2673(199902)72:2<171:NSOTTO>2.0.ZU;2-9
Abstract
The formation of micelles and aggregates in D2O solutions of the homologous series of surfactant cesium perfluoroalkanoates CnF2n+1COO-Cs+ (n = 5, 7, 9) and the other salts (Na+, NH4(+), and Rb+) of perfluorooctanoic acids we re studied at 30 and 50 degrees C by using some NMR techniques. The critica l micelle concentrations (cmc) were determined by F-19 chemical shift measu rements. The studies of Cs salts have shown that the effect of each CF2 gro up on micelle formation is roughly equivalent to that of 1.5 CH2 groups. Ex cept for the n = 5 system at 50 C-degrees, second breaks other than cmc at higher concentration were observed for alpha-CF2 groups of all Cs salts, wh ich suggest the transformation into a larger micelle, most likely ellipsoid al. In the case of omega-CF3 groups these second breaks were not observed. Support for the F-19 results was furnished by Cs-133 chemical shift studies . The perfluorooctanoate surfactants with the Cs+ as a counter ion showed t he behavior that was different from the other salts of the same chain lengt h. This could be explained in terms of electrostatic and hydrophobic intera ctions between the counter ions and the micelles. Additionally, the molecul ar motions in monomer and micellar states are discussed by means of the F-1 9 relaxation times of the fluorine nuclei in the micelles.