Behavior of Sodium Lauroyl Sarcosinate in Solution and Binary Mixtures by Means NMR

• Published in: Applied magnetic resonance Vol. 45; no. 4; pp. 353 - 364
• Main Authors: Popova, Maria V., Michel, Dieter
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01-04-2014; Springer Nature B.V
• Subjects: Aqueous solutions; Atoms and Molecules in Strong Fields; Binary mixtures; Binary systems; Isomers; Laser Matter Interaction; Micelles; NMR; Nuclear magnetic resonance; Organic Chemistry; Physical Chemistry; Physics; Physics and Astronomy; Sodium; Solid State Physics; Spectroscopy/Spectrometry; Spin-lattice relaxation; Surfactants; Mixed Micelle; Critical Micelle Concentration; Surfactant; Relaxation Rate; Nuclear Magnetic Resonance Line
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-014-0531-9

Measurements of the
1
H and
13
C chemical shifts as well as
1
H spin–lattice relaxation times of sodium lauroyl sarcosinate (SLAS) in aqueous solutions and mixed binary systems with co-surfactants were carried out at various concentrations. It will be shown that changes in the chemical shifts for the N–CH
2
groups in SLAS with increasing surfactant concentration can be used to estimate the ratio
p
cis
/
p
trans
of
cis
- and
trans
-isomers. The relative fraction
p
trans
of molecules in
trans
-configurations increases the most in a narrow concentration range 0.007–0.034 mol/l, i.e., at the transition from the monomeric state to the micelle. The ratio
p
cis
/
p
trans
asymptotically decreases with increasing concentration, reaching a constant value at concentrations significantly above the critical micelle concentration. Thus, the ratio can be related to the process of micellization. If micellization takes place, the
cis
-isomer starts to transform into
trans
-isomer because the
trans
-isomer is more favorable in micelles. Because of the smaller cross section of the polar group region, the
trans
-conformation can be more easily incorporated into the micelle. In summary, the occurrence of micellar aggregates at low SLAS concentration in mixed systems can be clearly inferred from the nuclear magnetic resonance spectra.