Analysis of water self-diffusion in polycrystalline lamellar systems by pulsed field gradient nuclear magnetic resonance experiments

Abstract

A study of the water self-diffusion in polycrystalline lamellar systems, by pulsed field gradient spin-echo (PFG-SE) nuclear magnetic resonance (NMR) experiments, is reported here. Our analysis confirmed the validity of previous equations for bidimensional water self-diffusion in lamellar lyomesophases and clarified their applicability limits. Depending on the diffusion experimental time range, two different procedures can be built up; for wide amplitude windows, the experimental diffusion coefficients are correlated to the fraction of bound water, whereas for short times it has been possible to point out the ‘‘obstruction factor’’ to diffusion. Experimental support for the theoretical findings was inferred by investigation of the lamellar mesophase of the binary system water/sodium-bis-2-ethylhexyl sulfosuccinate (AOT). It confirmed the existence of some defects in the lamellae at water concentration higher than 70 wt. %.

Measurement of the Principal Values of the Anisotropic Diffusion Tensor in an Unoriented Sample by Exploiting the Chemical Shift Anisotropy: 19F PGSE NMR with Homonuclear Decoupling

“…Depending on the source of the dominant dipolar broadening, one can use heteronuclear or homonuclear decoupling, of which the latter option is demonstrated here experimentally. In the present sample, the diffusion anisotropy would also be accessible, albeit in a longer experiment, via the large 13 C CSA of the carbonyl carbon (21).…”

“…Instead of exploiting the quadrupole coupling, the orientational dependence of the resonance frequency of spin I ϭ 1 2 nuclei via their chemical shift anisotropy is used to distinguish between domains with different orientation. Therefore, nuclei with substantial chemical shift anisotropy (6), like 19 F, 13 C, and 31 P, are the most feasible as a probe. Depending on the source of the dominant dipolar broadening, one can use heteronuclear or homonuclear decoupling, of which the latter option is demonstrated here experimentally.…”

Diffusion in Solid Proton Conductors: Theoretical Aspects and Nuclear Magnetic Resonance Analysis

“…However, if diffusion takes place, the diffusing nucleus will feel a change in the magnetic field and in the resulting phase it experiences, and the signal will be reduced. This change in phase results in attenuation of the magnetization M. In the case of free Gaussian diffusion, the theoretical expression of echo attenuation, for a selected NMR peak integral intensity, is given by the Stejskal-Tanner equation [17,22]: where D is the self-diffusion coefficient, g is the gradient strength (Gauss/cm or Tesla/m), and d and D are the time duration of the applied gradient pulse and the interval between gradient pulses, respectively. I(g) is the signal intensity at t ¼ 2t in the presence of gradient pulses of strength g, while I(0) is the intensity in the absence of any gradient pulses.…”

Modelling of high quality pasta drying: mathematical model and validation

“…6. Assuming a free Gaussian diffusion, the theoretical expression of echo attenuation F is given by the well-known StejskalTanner equation (Coppola et al, 1993) …”

“…The water diffusivity determination was carried out using PFGSE (Pulsed Field gradient Spin-Echo) 1H-NMR technique (Coppola, La Mesa, Ranieri, & Terenzi, 1993) with an usual pulse sequence consisting of a 90°radio frequency (rf) pulse at t = 0 followed by a 180°rf pulse at t = r; this results in a spin-echo at t = 2r. In addition to rf pulses, a pulsed magnetic field gradient is inserted on each side of the 180°rf pulse, causing the attenuation of echo intensities.…”