Relaxometry spin-lattice relaxation

In particular, in Ref. 78 the proton transfer dynamics of hydrogen bonds in the vicinity of the guest molecules has been studied by using a field-cyclic nuclear magnetic relaxometry (spin-lattice relaxometry). It has been revealed that the spin lattice relaxation incorporates the two major members ... 

Faster incoherent tunnelling processes can be studied by solid state NMR relaxometry [40, 41]. In these experiments the experimentally determined spin-lattice relaxation rates are converted into incoherent exchange rates. The latter are then evaluated, for example with the Bell tunnelling model described above. 

Xu et al. investigated the interaction of water with NAFION under acid, sodium, and potassium forms using NMR relaxometry techniques in terms of dispersion R co) reveahng two types of bound water, the expected bound water and water with considerably reduced mobility in the driest NAFION [105]. Lee et al. applied NMR spin-lattice relaxation techniques to characterize the molecular motion of H20 in NAFION 117, AQUIVION E87-05, and sulfonated-RADEL proton exchange membranes [106]. It was concluded that the motion of H20 is affected by the acidity and mobihty of the sulfonic acid groups to which the water molecules are coordinated at low hydration level. At higher levels of hydration, the molecular motion of H20 is affected by the phase separation of the hydrophihc/hydrophobic domains and the size of the hydrophilic domains. 

The polar coordinates r, (p define the internu-clear vector of the spin system. That is, any molecular motion affecting these coordinates leads to fluctuations of the functions so that the spin-lattice relaxation rate (Eqn [1]) directly reflects these motions via the intensity and autocorrelation functions. The prominent goal of NMR relaxometry, hence, is to monitor the features of molecular dynamics. This is best done by recording the frequency dependence of spin-lattice relaxation. 

The term relaxometry is normally used in context with techniques for the measurement of spin-lattice relaxation times in general. Transverse relaxation and effects due to residual dipolar couplings will be considered in the next section. 

Spin-lattice relaxation dispersions according to Eq. 30 can be recorded over several decades of the frequency with the aid of field-cycling NMR relaxometry [18-21]. Combined with ordinary high-field NMR relaxometry, the accessible ranges for protons and deuterons are... 

Fig. 4. Schematic representation of a typical cycle of the main magnetic field Bo employed with field-cycling NMR relaxometry. The free induction decay (FID) is recorded after a 90° radio frequency (RF) pulse in the detection field. The repetition time amounts several times the spin-lattice relaxation time in the polarization field. The most critical sections of the cycle are brought out by gray boxes...

Field-cycling NMR relaxometry experiments can be favorably supplemented by ordinary high-field relaxation measurements employing the inversion-recovery or saturation-recovery variants. Comparative spin-lattice relaxation experiments in the rotating frame (Tip) are also of interest particularly in the presence of molecular order [22]. A detailed description of the diverse NMR methods referred to can be found in Ref. [2]. 

Fig. 14a-d. Proton spin-lattice relaxation time of various polymer melts as a function of the inverse temperature for different molecular masses and frequencies. The conclusion is that field-cycling NMR relaxometry of these polymers at the experimental temperatures is largely dominated by (OXs as a condition for the observation of components B and potentially C. a Polydimethylsiloxane (PDMS) for different frequencies. Tj is too short in the temperature range indicated to fulfill the minimum condition even at... 

Figure 16 shows typical proton spin-lattice relaxation dispersion data for polyethylene melts as an illustration of the three-component behavior of polymer melts. For comparison with model theories the chain-mode regime represented by component B is suited best and will be discussed in detail. It will be shown that the NMR relaxometry frequency window of typically 10 Hz< V <10 Hz (for proton resonance) almost exclusively probes the influence of chain modes represented by component B (compare Fig. 5). That is, the correlation function experimentally relevant for spin-lattice relaxation dispersion may be identified with component B according to...

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