Rotating frame spin-lattice relaxation measurements

ROTATING FRAME SPIN-LATTICE RELAXATION MEASUREMENTS 

We can understand spin-lattice relaxation in the rotating frame by first understanding the experiment to observe this process. It is done by the following technique or some variation of it. The sample is placed in a large applied field Hq 

Two things should be noted First, the relaxation rate 

Several other techniques have been developed to prepare the spin system in the spin-locked condition. One technique does not require phase-shifting the rf. An rf pulse exactly 

Note that before the 90° pulse is applied, the spin temperature equals the lattice temperature. If the process of spin locking is achieved in a time short in comparison to T or Tlp Mo is preserved in magnitude. If M is now to be 

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IV.C.l. ROTATING FRAME SPIN-LATTICE RELAXATION MEASUREMENTS... 

Han et al. studied the dynamics of hydrated water molecules in NAFION by means of high-resolution MAS NMR measurements. Bound and free states of hydrated water clusters as well as the exchange protons were identified from the NMR chemical shift measurements, and their activation energies were obtained from the temperature-dependent laboratory- and rotating-frame spin-lattice relaxation measurements. Besides, a pecufiar motional transition in the ultralow frequency region was observed at 373 K for the free hydrated water from the rotating-frame NMR spin-lattice relaxation time measurements [60]. 

Jonas et al. measured the proton rotating frame spin-lattice relaxation time (Tip) at pressures from 1 bar to 5000 bar and at temperatures of 50 to 70 °C for DPPC and at 5 to 35 °C for POPC. If intermolecular dipolar interactions modulated by translational motion contribute significantly to the proton relaxation, the rotating frame spin-lattice relaxation rate (1/Tip) is a function of the square root of the spin-locking field angular frequency... 

The rotating-frame spin-lattice relaxation time for protons, Tip,( H), was measured indirectly from CPMAS/DD NMR to probe possible molecular scales of heterogeneity in the miscible poly(benzyl methacrylate)/poly(ethylene oxide) blend over the whole composition range. ... 

The NMR rotating frame spin-lattice relaxation time (Tjp) method, which has been used successfully in our laboratory in studies of pressure effects on diffusion in highly viscous liquids, was used in this study to measure lateral diffusion of the phospholipid molecules in DPPC and POPC vesicles. An advantage of this method is that the diffusion coefficient is found directly from measured quantities without estimations of molecular parameters or the effects of the addition of spin or fluorescence probes to... 

NMR rotating-frame spin—lattice relaxation time measurements revealed in a sensitive manner the evolution of the microscopic environment and proton dynamics of the two distinct hydrogen bond types in the system, compatible with the electrical conductivity and the impedance spectroscopy measurements. In addition, the reorientational motion of the PO4 tetrahe-dra, as revealed by rotating-frame NMR, is coupled to the proton dynamics [118]. 

Pulse sequence used to measure the rotating frame spin-lattice relaxation time. (Figure from reference 3.)... 

Polymer Dynamics. 13C spin-lattice relaxation times (Ti) were determined with either an inversion-recovery sequence (16) (for carbons observed by direct polarization) or with a modified cross-polarization experiment (17). 13C rotating-frame relaxation times (Tip(C)) were derived from measurements of the carbon signal that remained after a Tjp(C) hold time of... 

Complementary NMR measurements, such as rises of carbon polarisation in a spin-lock experiment and determination of 13C spin-lattice relaxation times in the rotating frame, Tip(13C), support these conclusions about the correlation times of the side-ring CH and CH2 motions in the various poly(cycloalkyl methacrylates). 

The temperature dependencies of the ( 172)0/ 1/2 ratio, where ( 1/2)0 is the 1/2 value measured at room temperature, determined for the CHOH - CH2 - O and CH2 - N units of the hydroxylpropyl ether (HPE) sequence (Fig. 92) in the HMDA network [63] are shown in Fig. 97. It is worth noticing that the 1/2 values of these two types of carbons have the same temperature dependence. Up to 60 °C, the 1/2 values are constant and equal to the rigid-lattice values, indicating that the HPE sequence does not undergo any local motion at a frequency equal to or higher than 105 Hz in this temperature range. Above 60 °C, mobility develops, which leads at 100 °C to motions in the tens of kilohertz for the whole HPE sequence. These results are qualitatively confirmed by data on 13C spin-lattice relaxation time in the rotating frame, Tip(13C). 

In order to probe lower frequency motions, some relaxation measurements are made in instruments designed to allow relaxation to occur at very low magnetic field, where the Larmor frequency is a fraction of a MHz. Alternatively, it is possible to define and measure a spin-lattice relaxation time in the rotating frame, given the symbol Tlp, Which is sensitive to motions in the kHz range. We shall return to Tlp in Chapter 9. 

Chang et al. reported the miscibility of poly(vinylphenol) (PVPh) with poly(methyl methacrylate) (I MMA) Figure 1 shows the C CP/MAS spectra of pure PVPh, PMMA, PVPh-co-PMMA, PEG, and PVPh-co-PMMA/ poly(ethylene oxide) (PEO) blends of various compositions with peak assignments. VPh contents of PVPh-co-PMMA is 51 mol% and Mn of PEO is 20,000. The spin lattice relaxation time in the rotating frame (Tip ) was measured to examine the homogeneity of PVPh-co-PMMA/PEO blends on the molecular scale. 

The miscibility of poly(methyl acrylate) (PMAA, Mw= 150,000)/PVAc (Mw= 167,000) blends at various mixing ratios was investigated by both Ti and Tip measurements. C CP/MAS NMR spectra of PMAA, PVAc and the PMAA/PVAc blends are shown in Fig. 2. Figure 3 shows the plots of the spin-lattice relaxation times in the laboratory (Ti , A) and in the rotating (Ti, B) frames against the molar ratio of PMAA (xpmaa)-The ll relaxation times from the CI 12 (O) and OCH (A) carbons for PMAA and PVAc, respectively, can be observed because these two carbons are observed separately even in the blends (Fig. 2), so that it is possible to obtain each relaxation time for PMAA or PVAc in the blends independently. 

Crystalline a-D-galacturonic acid monohydrate has been studied by C CPMAS NMR and X-ray crystallography. The molecular dynamics have been investigated by evaluating C spin-lattice relaxation in the rotating frame (Tip) and CSA properties of each carbon. It has been found that only limited molecular motions can be detected in the low frequency (<10 Hz) range by Tip( C) measurements and changes of CSA properties as a function of temperature. 

A cured epoxy synthesised from a mixture of the diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylenediamine was studied by NMR spectroscopy including multiple pulse techniques and spin-lattice relaxation in the rotating frame. Tip. The study [28] focused on the water distribution based upon possible variation in the cross-link density measured by spin diffusion. From the analysis involving a combination of Tip and multiple... 

Fluorine-19 spin-lattice relaxation times in the laboratory frame, Ti, and and spin-lattice relaxation times in the rotating frame. Tip, were measured under high-resolution conditions (i.e., selectively) at ambient probe temperature ( 23°C), and are reported in Table 18.3. 

The dynamics of intact lime cuticle and its two major component polyesters, cutin and wax, have been studied by the MAS NMR experiment [134]. By the measurements of spin-lattice relaxation times and spin-lattice relaxation times in the rotating frame which characterize respectively the megahertz- and kilohertz-regime motions, it is indicated that motional restrictions are present at the crosslinks of the cutin polymer and along the alkyl chains of the wax. The values of relaxation times, which differ for analogous carbon sites of cutin and wax individually, approach common values for the two materials in the intact lime cuticle. These results are considered to provide evidence for hydrophobic association within the plant cuticle of the long aliphatic chains of cutin and wax. 

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