Combined use of NMR relaxation times and self-diffusion coefficients for characterizing solvent bound to cetyltrimethylammonium bromide micelles in water and formamide

Abstract

Micellar solutions of cetyltrimethylammonium bromide, with D20 or formamide (FA) as solvent, have been studied through longitudinal NMR relaxation (170 and 12 34H for D20; 13C, 170, 14N, and 15N for FA) and self-diffusion measurements. Both determinations concern only the solvent molecules. The data are analyzed on the basis of a fast exchange between two states; free solvent and solvent molecules bound to micelles. From these measurements, we derive structural and dynamic information about (i) the relaxation rate of the solvent (D20, FA) in the bound state, (ii) the number n of solvent molecules per surfactant polar head, (iii) the possible variation of micelle size in water and formamide, and (iv) reorientational features of the solvent (FA, D20) in the bound state and in the free state.

The Alignment of Lyotropic Liquid Crystals Formed by Hexadecyltrimethylammonium Bromide in D2O in a Magnetic Field

“…The assumption of T 2 a = T 2 c = T 2 f /10 is rather arbitrary. The experimental spectra can also be simulated using other ratios of p f / p a and T 2 f / T 2 a . Nevertheless, the major conclusion from the simulation should be valid: the asymmetry of the 2 H NMR spectra is a result of different chemical shifts of the bound and free D 2 O molecules.…”

Micellization of N-Alkylpyridinium Halides in Formamide Tensiometric and Small Angle Neutron Scattering Study

“…Their purity was checked by 1 H and 13 C NMR and microanalysis. Their water content was determined by the Karl Fischer method (Mettler DL18 instrument) and was found to be below 0.1% after freeze-drying (lyph-Lock apparatus) …”

“…Micellization of ionic surfactants in nonaqueous polar solvents has been investigated by numerous authors. − The two parameters controlling this process are now well established: (1) The solvents must have a cohesion energy density (ced) above 1.1 J·m -3 . , We demonstrated in a study using N -methylsydnone as a cohesive but aprotic solvent that hydrogen bonding is not essential …”

Investigation of the Structure and Dynamics of Surfactant Molecules in Mesophase Silicates Using Solid-State 13C NMR

“…NMR techniques have been used extensively to characterize the structure and dynamics of liquid crystal surfactants used in the synthesis of mesoporous ceramics as well as their phase diagrams. [6][7][8][9] However, few studies have been reported regarding the nature of the interactions between surfactants and silicate precursors which evolve mesoporous silicates. Phase transformations in surfactant-silicate systems have been studied using 2 H and 15 N NMR, 5,10 while 29 Si NMR has been used to study the degree of silicate condensation and the structure of the Langmuir 1996, 12, 2663-2669 S0743-7463(95)01515-0 CCC: $12.00 © 1996 American Chemical Society mesophase silicates.…”

“…Nuclear magnetic resonance (NMR) spectroscopy experiments provide one route to understanding the three major phenomena involved in the synthesis of mesoporous ceramics: (1) the assembly of surfactant systems into a liquid crystal array, (2) the formation of ceramic phases via nucleation and growth of soluble inorganic precursors, and (3) the interaction chemistry between the surfactant, inorganic precursors, and both liquid crystal and ceramic phases. NMR techniques have been used extensively to characterize the structure and dynamics of liquid crystal surfactants used in the synthesis of mesoporous ceramics as well as their phase diagrams. − However, few studies have been reported regarding the nature of the interactions between surfactants and silicate precursors which evolve mesoporous silicates. Phase transformations in surfactant−silicate systems have been studied using 2 H and 15 N NMR, , while 29 Si NMR has been used to study the degree of silicate condensation and the structure of the mesophase silicates. ,,, The 13 C spectra have been reported for surfactants in as-synthesized mesoporous materials. , There has been no detailed study reported using 13 C NMR to probe the structures and dynamics of surfactant molecules in mesophase silicates.…”