Pulse gradient spin-echo measurements

Diffusion and Pulsed Gradient Spin Echo Measurements... 

J. D. Seymour, B. Manz, P. T. Callaghan 1999, (Pulsed gradient spin echo nuclear magnetic resonance measurements of... 

The solvent mobility in atactic polystyrene-toluene solutions has been studied as a function of temperature using NMR. The local reorientation of the solvent was studied using deuterium NMR relaxation times on the deuterated solvent. Longer range motions were also probed using the pulsed-gradient spin-echo NMR method for the measurement of diffusion coefficients on the protonated solvent. The measurements were taken above and below the gel transition temperatures reported by Tan et al. (Macromolecules, 1983. 16, 28). It was found that both the relaxation time measurements and the diffusion coefficients of the solvent varied smoothly through the reported transition temperature. Consequently, it appears that in this system, the solvent dynamics are unaffected by gel formation. This result is similar to that found in other chemically crossed-linked systems. 

The self-diffusion coefficient measurements were made using the pulsed-gradient spin-echo (PGSE) method which has recently been reviewed (JLL). For a nucleus in an isotropic solution, the PGSE-NMR normalized signal intensity, 1/1q is given by ... 

PGSE pulsed-gradient spin echo method of measuring self-diffusion,... 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

A Multiscale Analysis of 1H Pulsed Gradient Spin-Echo NMR Measurements. 

PULSED-GRADIENT SPIN-ECHO (PGSE) NMR FOR MEASUREMENTS OF SELF-DIFFUSION COEFFICIENTS... 

Figure 5.1 Pulsed-gradient spin-echo NMR sequence for the measurement of self-diffusion coefficient.

Stilbs P. Fourier transform NMR pulsed-gradient spin—echo (FT-PGSE) selfdiffusion measurements of solubilization equilibria in SDS solutions. J Colloid Interface Sci 1982 87 (2) 385-394. 

The dynamic characteristics of adsorbed molecules can be determined in terms of temperature dependences of relaxation times [14-16] and by measurements of self-diffusion coefficients applying the pulsed-gradient spin-echo method [ 17-20]. Both methods enable one to estimate the mobility of molecules in adsorbent pores and the rotational mobility of separate molecular groups. The methods are based on the fact that the nuclear spin relaxation time of a molecule depends on the feasibility for adsorbed molecules to move in adsorbent pores. The lower the molecule s mobility, the more effective is the interaction between nuclear magnetic dipoles of adsorbed molecules and the shorter is the nuclear spin relaxation time. The results of measuring relaxation times at various temperatures may form the basis for calculations of activation characteristics of molecular motions of adsorbed molecules in an adsorption layer. These characteristics are of utmost importance for application of adsorbents as catalyst carriers. They determine the diffusion of reagent molecules towards the active sites of a catalyst and the rate of removal of reaction products. Sometimes the data on the temperature dependence of a diffusion coefficient allow one to ascertain subtle mechanisms of filling of micropores in activated carbons [17]. 

Li pulsed gradient spin-echo (PGSE) measurements on LiPPh2 in thf or Et20 solutions show that the compound is a monomer in the former, but a dimer in the latter solution.9 Proton NMR chemical shifts have been used to examine perturbations in water structure in LiOH, KF or KC1 solutions.10... 

Zhu XX, MacDonald PM, Pulsed-gradient spin-echo NMR measurements of the diffusion coefficients of ketones in poly(methyf methacrylate). Maeromolecules 1992 25, 4345. 

PGSENMR Pulsed gradient spin echo NMR for self-diffusion measurements... 

Belfort and Segvers (unpublished results) have seen for adsorbed water in 24 A diameter porous glass, reductions in the measured (by pulsed gradient spin echo NMR) water self-diffusion... 

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