Spin probe mobility above

The spin probed ESR spectra of extracted sol and gel phases of the high molecular weight NR matrix are displayed in Figure 25.9 in order to probe the ESR spectra of slow component above Tg, which reflects the restricted motion of entangled and physically crosslinked NR chains (gel phase). The ESR spectra of the gel phase are characteristic of restricted NR chains below Tg with a constant value, whereas the ESR spectra of the sol phase indicate a continuous increase in mobility of spin probes with increasing temperature. The existence of a broad component in the isolated sol phase of the NR matrix confirms the presence of a certain extent of heterogeneity in the movement of spin probe above Tg. However, the intensity of the broad component in the sol phase disappears at a much faster rate at higher temperatures by the expense of the narrow component as compared with the behaviour of the extracted gel phase. 

ESR spectra of spin probe for NR/nanoclay nanocomposites at 100 and 110 °C are shown in Figure 25.39. ESR spectra of probe for NR/nanoclay nanocomposites measured at temperature above 80 °C show broad lines along with the usual narrow line, which were also reported in the NR/nano-silica nanocomposites. These observations confirm that the mobility of the spin probe is restricted in presence of nanoclay. 

As is seen, the values are well described by the above function with the parameters E = 34.7 kj-mol" and log x = -14.2. It was assumed that the aminoxyl fragment participates in a sufficiently rapid cooperative motion involving the aminoxyl group and several carbon atoms of the main chain linked to this group. This additional mobility produces additional averaging of A and g-tensors to virtually an isotropic level. For this reason, the correlation times estimated in the considered system are close to the x values for the rotation of spin probes determined by the motion of molecular segments. 

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. 

Aluminum clusters have been investigated using a variety of experimental techniques, providing abundance spectra [164, 165], spin multiplicities [166], IPs [164, 167], EAs, and static polarizability [105]. Reactivity studies have been reported for size-selected A1 clusters in contact with a variety of small molecules (see, for instance, [167]), and the presence of different isomers in a population of clusters has been investigated by measuring the mobility of clusters in a buffer gas [168]. Finally, the electronic structure of these clusters has been probed by photoelectron spectroscopy on the anion species Al [169, 170]. As mentioned above, bulk aluminum is remarkably close to a nearly... 

---