Extrema separation

Figure 6.30. Enhancement of the proton NMR signal amplitude (P/P -l) is shown as a ftinction of microwave frequency as taken by the dynamic nuclear polarization experiments, where P and / are the signal amplitude with and without microwave pumping, respectively [143,146,173,174], The Overhauser effect (OE) typical to the mobile spins makes a shaip peak at the Lannor frequency cve of the electron spin but the Solid State Effect (SSE) shows two extrema separated by o from (O charactcrictic with the fixed paramagnetic spins [8], The solid curves are a guide for the eye. (a). t a is-(CH), (A//pp 0.8 G) and , trs-rich (CH)> (Affpp 7.8 G) 1174]. (b) The temperature dependence of the peak-ratio in //ww-(CH), 173], y/x = 0 means pure Overhauser enhancement and y/x— 1, the solid slate effect [173]. Note the change from the mobile above 150 K to the trapped below 150 K, Most of the solitons are trapped below 10 K, (after (a) [174] and (b) [173])...

Figure 8 Extrema separation of ESR spectra of NO radical dissolved in PBLG.

The temperature dependence of ESR spectra of fractured polyethylene labelled by nitroxide radicals is shown in Fig. 10.2., which shows the case of high density polyethylene. W indicated in Fig. 10.2. means extrema separation (outermost separation) and is the same quantity as S in Eq. (9,5). W is a measure of the mobility of the materials and the value of W is shown to decrease with raising temperature reflecting a much more mobile character of the observed molecules at elevated temperatures. As mentioned in the previous section, the varying extrema separation with temperature has been widely discussed in connection with molecular motion. 

Fig. 10.2. ESR spectra of high density polyethylene fractured in the presence of nitrosobenzene. Observation temperatures are shown on respective spectra. W is extrema separation (outermost separation width) (Ref. )...

Fig. 10.6. Variation of extrema separation with temperature of observation for high density polyethylene fractured for I h (A), 4 h (A), 10 h ( ), and 25 h (O) (Ref. )...

Fig. 10.7. Variation of extrema separation with temperature for high density (O) and low density ( ) polyethylenes (Rcf. >)...

Fig. 10.8. Extrema separation vs. temperature of fractured atactic polypropylene labeled with nitroxide radical O, before melt , after melt (Ref )...

Fig. 10.11. Variation of extrema separation of ESR spectra with temperature thermally degraded materials, (O) first heating and ( ) second heating y-irradiated materials (A) first heating and ( ) second heating (Ref. )...

Furthermore, it is desirable to make a more detailed investigation of the nature of the molecular motion reflected in the narrowing of the extrema separation of ESR spectra. Here, a rather detailed analysis of the temperature dependence of the ESR spectrum of irradiated materials labelled by the spin trapping method will be described. 

As for the molecular motion in the polyethylene chain in UPEC (Sect. 8), the temperature dependence of the line width of the spectrum coming from nitroxide radicals was studied by means of computer simulation. In order to simplify the procedure, line widths of the central component of the main triplet at various temperatures were obtained and are plotted against the observation temperature together with the extrema separations, as shown in Fig. 10.12. The original plots have been somewhat simplified. The values obtained in the first and second heating are shown in the same... 

Fig. 10.12. Variations of line width and extrema separation with observation temperature of y-irradiated materials labeled with nitroxide radical (Ref )...

Fig. 10.13. Correlation time as a function of the inverse temperature Estimated from line width (O) estimated from extrema separation based on Brownian diffusion (A), moderate jump ( ) and strong Jump ( ) (Ref. )...

Fig. 10.14. Plots of correlation times estimated from line width (x) and extrema separation (moderate jump) (A) on the relaxation map arranged from mechanical and dielectric data (--------------(Ref.

Fig. 10.16a and b. Effect of diluent on temperature dependence of extrema separation width (a) for thermally degraded materials and (b) for y-irradiated materials (Ref. )... 

The effect of the diluent, tetrachloroethylene, to the narrowing curve of extrema separation for T was examined, leading to Fig. 10.16b. i.e., the effect of the diluent is to shift the narrowing temperature downward. This is quite consistent with the results obtained by Kakizaki and Hideshima because the transition in T was inter-... 

The first term represents the field-independent background, the second denotes a Lorentzian with FWHM AB = hlgu T, and third one describes a dispersion curve with the extrema separation AB = hlgfi r... 

Figure Plot of extrema separation versus temperature diowing T50C...

Figure 3 shows an idealized plot of the variation of extrema separation with temperature for a nitroxide-doped polymer sample. Representative ESR spectra for three characteristic temperature ranges appear as insets. The T qq parammer has been empirically correlated with accepted literature values of the glass transition temperamre for a wide range of polymers, running... 

Fig. 3. niustiative plot of extrema separation versus temperature for a spin probe doped polymer sample. The temperature at 50 gauss extrema separation, T qq, corresponds to the glass transition tempoature at the ESR operating frequency. The variation in the sharpness and symmetry for die three-line spectra of a nitroxide spin probe are shown as insets for three characteristic temperature ranges (see text). After Boyer, refs. 6 and 13. 

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