Nuclear relaxation time images by radiofrequency field gradients applied to the study of solvent permeation into polymeric materials.

T(2) images are obtained by two interleaved B(1)-gradient imaging experiments preceded by CPMG trains of different lengths. The method is assessed by means of a phantom involving compartments of different, though relatively close, T(2) values. T(1) images arise from a previously published procedure also based on two interleaved B(1)-gradient imaging experiments involving different evolution of the longitudinal magnetization. Both types of image appear to be useful in view of the structural characterization of polymer samples through the T(2) and T(1) distribution of a solvent embedded in the material.

Visualization of residual anisotropic interactions in crosslinked natural rubbers by dipolar local field measurements and 2H natural abundance NMR spectroscopy.

An extension of the exploitation of indirect observation of 1H nuclei through 13C resonances is presented in the case of crosslinked elastomers. It is demonstrated that, by using this method in vulcanized elastomers above Tg, a direct visualization of residual dipolar interactions on different functional groups as well as their dependence on motional constraints is available. It is also shown that 2H natural abundance NMR spectra of elastomers provide similar information on motional constraints by way of residual quadrupolar interactions.

Magnitudes and mutual orientations of dipolar and shielding interaction tensors determined from the orientation dependence of spinning sidebands of slowly rotating powder samples.

It is shown that the orientation dependence of spinning sidebands of slowly rotating solids can be exploited to determine with good precision the heteronuclear bond distances and mutual orientation of dipolar and shielding tensors from a single dipolar modulated chemical shift anisotropy spectrum. The method is based on the dynamics of polarization transfer in the initial period of tens of microseconds, and may be useful in solids with relatively isolated groups of spins.

Chemical shift imaging in rotating solids by radiofrequency field gradients

A dedicated equipment has been designed for solid state NMR imaging in the spatial direction coinciding with the rotation axis of a 13C CP/MAS probe. It involves a two-turn B1 gradient coil whose plane is perpendicular to that axis and a 1H-13C doubly tuned saddle coil used for normal spectroscopic operations, orthogonal to the latter. The experiment provides a two-dimensional diagram with 13C chemical shift in one dimension whereas the second dimension corresponds to the space variable. Some test experiments demonstrate the validity of this approach. Copyright 1998 Academic Press.

Self-Diffusion Measurements by Carbon-13 NMR Using Radiofrequency Field Gradients

This paper demonstrates the feasibility of self-diffusion measurements by radiofrequency field gradients with equipment tuned to the carbon-13 resonance frequency (i.e., 50 MHz for a field of 4.7 T). For the first time, self-diffusion coefficients of carbon disulfide and carbon tetrachloride are measured by NMR. The agreement with results from tracer methods is excellent. Copyright 1998 Academic Press. Copyright 1998 Academic Press

ODESSA, a New 1D NMR Exchange Experiment for Chemically Equivalent Nuclei in Rotating Solids

A new 1D NMR exchange experiment in the slow-motion regime of spinning solids, with chemically equivalent nuclei exhibiting quadrupole coupling or chemical-shift anisotropy, is proposed. It consists of the usual three-pulse sequence for 2D exchange spectroscopy, P1-t1-P2-taum-P3-t-acquisition, but with the evolution time fixed at one-half a spinning period, t1 = TR/2, and a mixing time equal to an integer multiple thereof, taum = GTR. The magnetic polarizations associated with the various spinning sidebands are then polarized in alternate directions at the beginning of the mixing time. Dynamic processes during taum redistribute the polarizations, resulting in modified sideband patterns during the detection time, t. Experimental results are presented for carbon-13 and deuterium in dimethyl sulfone, which undergoes molecular reorientation in the solid state. The results are compared with simulations which include the effect of reorientation and longitudinal relaxation.