Relaxation time deuterium NMR

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 method employed for the evaluation was determination of deuterium NMR relaxation times as a measure of molecular motion. If radial differences in concentration, or solvation were present such that the segmental mobility of the structure varied significantly between layers, measurable changes in Tt and T2... 

The behavior of methine-labeled poIy(ethyl acrylate)-di (PEA-di), poly(wo-propyl acrylate)-di (PIPA-di), and poly(n-butyl aciylate)-di (PNBA-di) has been studied with deuterium NMR relaxation time measurements in concentrated solutions with chloroform. PEA-di and PNBA-di behaved similarly in terms of solution dynamics, but PIPA-di was found to reorient significantly faster at similar concentrations. The relaxation times were fitted to a log-normal distribution of correlation times and the resulting mean correlation times fit to Arrhenius behavior. The energies of activation were found to increase with increasing concentration from about 6 kJ/mol at lower concentrations to 10-20 kJ/mol from about 40 to 80 wt % polymer. 

In our laboratory, we have found that the use of deuterium NMR relaxation times could provide a convenient probe of local segmental motions in concentrated solutions. The overlap of different moieties can be avoided through the use of specific labeling. The low natural abxmdance of deuterium means that only the labeled sites will give any appreciable amount of signal. The moderate size quadrupole moment of the deuteron means that the relaxation of deuterons attached to carbons can be interpreted in terms of the reorientation of the C-D bond vector. Additionally, the relaxation times of deuterons on polymers tend to be quite rapid so that the experiments can be done quickly. 

Carbon-13 NMR has been used to study anisotropic rotational motion in liquids, as have combinations of techniques. Gillen and Griffiths (1972) have obtained the two reorientational relaxation times for benzene (a symmetric top) by combining reorientation relaxation times obtained from Raman band shapes and deuterium spin-lattice NMR relaxation times. The most extensive series of measurements probing anisotropic molecular reorientations have been made by Pecora and co-workers (Alms et al., (1973a, b)), who combined Carbon-13 spin lattice relaxation times with those obtained from depolarized Rayleigh spectra. 

The deuterium NMR spectra of toluene-d0 in aPS solutions consists of two resonances which are resolved and assigned to the methyl and aromatic groups. In these solutions spin-spin or dipolar couplings are small and consequently are not observed. As the temperature is lowered, the aromatic resonance systematically broadens while the methyl resonance remains relatively constant in width. The linewidths of the aromatic resonances are the same as those which would be predicted from the T2 measurements reported below. The separated resonances make it possible to determine the relaxation times of each type of resonance. 

Deuterium nmr describes in equally clear-cut and elegant a manner the static (order parameter) and the microdynamic (correlation time t ) properties of hydrocarbon chains in aggregated surfactants 13). The example of octanoate, in various phases, resembles the membrane behavior of phospholipids a decrease of the order parameter is found for deuterium relaxation rates,... 

Deuterium diffusion was studied in VDX, where 0.4 < x < 0.6, by means of 2H NMR measurements.599 1H and 51V spin-lattice relaxation times for TaV2Hx, where x < 0.18, were consistent with two co-existing proton-jump processes.600 3H, 2H and 51V spin-lattice relaxation times were also determined for NbVCrHo.3, NbVCrD0.3g and NbV 14Cro.6Ho.6 in the temperature range 11-424 K.601 A DFT/broken symmetry approach has been used to study exchange... 

Mobility of water in cellulose has been studied by solid-state and high-resolution NMR as a function of moisture content within the unfreezable moisture range (0-19% dry basis).Measurements of relative mobilities were based on relative intensities, transverse and longitudinal relaxation times and line shape analysis. At 2-16% moisture content (dry basis), water molecules reoriented anisotropically, suggesting an interaction with cellulose fibers. At moisture content below the monolayer value (2.8%, dry basis), 90% of the protons were immobile and no liquid deuterium signal was detected. A sharp increase in liquid or mobile intensity (accompanied by a decreased LW) and increases in NMR Ti and T2 relaxation times were observed as moisture increased above 9% (dry basis). 

Top) Solid-state proton (left) and deuterium (right) NMR spectra for freeze-dried media systems containing 14% mannitol indicating narrow (rapidly exchanging) and broad (slowly exchanging) components. (Bottom) Tj and T2 deuterium relaxation times for freeze-dried xanthan-locust bean gum with (solid circles) and without (solid squares) 14% mannitol. 

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