Relaxation time measurements for

Equation 24.20 gives -y = 1.4 0.1. The relaxation times measured for this material at P = 0.1 MPa [82] in combination with the EOS for the mbber [81] enable the value of 7V associated with each... 

It is interesting to note in Figs. 13 and 14 that the relaxation behavior of PS(OH)-18/PMMA and PS(OH)-4/PMMA is indistinguishable. However, as shown in the next section, these blends have quite different chain arrangements. This implies the limitation of routine NMR relaxation time measurements for monitoring the blend structure at the molecular level. 

Table 17 presents relaxation time values characterizing the intramolecular mobility of various fragments of cholesterol-containing polymers with LM in various solvents9. As is seen, the values of relaxation times measured for the same polymer in various solvents differ significantly, which reflects the specificity of conformational state and intramolecular organization. 

In early years of NMR, extensive studies of molecular dynamics were carried out using relaxation time measurements for spin 1/2 nuclei (mainly for 1H, 13C and 31P). However, difficulties associated with assignment of dipolar mechanisms and proper analysis of many-body dipole-dipole interactions for spin 1/2 nuclei have restricted their widespread application. Relaxation behaviour in the case of nuclei with spin greater than 1/2 on the other hand is mainly determined by the quadrupolar interaction and since the quadrupolar interaction is effectively a single nucleus property, few structural assumptions are required to analyse the relaxation behaviour. 

Table 7 lists the DQCC values calculated directly from the T j relaxation times measured for the (Dj) ligands of transition metal dihydrogen complexes in solution. These values have been calculated by eq. (3) with the assumption of Tj being zero or varying between 0 and 1. All these DQCC values are remarkably smaller than those of classical hydride systems (see Table 3 and 4). They also differ significantly from the values predicted by MO calculations (Table 6). Probably the DQCC values in Table 7 are reduced due to the presence of fast (D2) motions. According to H solid state NMR, the motions are present even at lowest temperatures in the solid state [22].

The model described earlier assumed that wd was very large and h c was very small. Relaxation time measurements for water in rocks found that Ti and T2 were almost independent of temperature in the range 25-175 °C. This suggests that diffusion is not playing a significant role, and so supports the fast-exchange assumption. It thus appears that molecules sample only a limited volume of pore space before they are relaxed in the case of water in rocks. However, the diffusion and pore-coupling rates may be important in other systems. 

NMR methods offer a noninvasive method of characterizing porous media. A variety of different techniques may be used to obtain useful information on the pore space. For instance, pore sizes may be measured using the freezing point depression technique for mesoporous solids or by relaxation time measurements for macroporous solids. Other pore space information comes from PFG techniques, while direct imaging of the pore space is possible for large pores. The information from studying the pore space can then be incorporated into appropriate pore network models. 

Finally it is interesting to point out the good agreement between correlation times 2 and 3 in Figure 3. Correlation time 3 has been computed from the diffusional contribution to the proton spin-lattice relaxation time measured for the CD OH - X OH system, after the proton exchange contribution has been removed, whereas correlation time 2 has been obtained, in a straight forward manner, for the CH OD-X-OD system. 

The principal relaxation times measurable for resolved resonances from solution state samples are the spin-lattice relaxation time (T ) and the spin-spin relaxation time (T2). Spin echo methods may be used to measure T2 values and these are often useful in defining chemical exchange rate processes. values are readily obtained from the inversion-recovery experiment and can be directly used to provide structural information. For nuclei with spin I = 1/2 in diamagnetic molecules in solution there are two principal mechanisms which contribute to the rate of the relaxation namely the dipole-dipole inter-... 

I begin this section by referring to the work on surfactants in solution and micellar and related systems. Popova and co-workers " reported relaxation times measurements for Na for sodium octanoate in aqueous solution and aqueous dispersions of silica. Concentration and... 

We begin with the work where the studied fluid was different than water. Some papers have dealt with gases contained in the porous materials. Yager and co-workers reported relaxation time measurements for He adsorbed in the pores of mesoporous molecular sieve MCM-41 at low temperatures (down to 1.7 K) and at a range of frequencies. They observed the behaviour, characteristic for one-dimensional... 

Rotational relaxation times measured for several membrane proteins, mostly by the triplet phosphorescence method, are given in Table 1.5. Clearly some integral proteins rotate rather rapidly in membranes. The rotational relaxation time is defined by = 1/D where D is the rotational diffusion coefficient referred to... 

Figure 2 shows the relationship between the formula weight of the dendrimers and the C-NMR relaxation time measured for the carbons of the ter-... 

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