Dielectric loss peak intensity

In view of Table II the main difference of the parameters, fitted for HW, from those, fitted for OW, concerns (i) some increase of the libration amplitude / , (ii) decrease of the form factor /, (iii) decrease of the frequency vq (the center frequency of the T-band) and increase of the moment nq, responsible for this band, and (iv) decrease of the intensity factor gj, which strongly influences the THz band. Comparison of curves 3 in Figs. 4h and 5h shows that the partial dielectric loss peak g"max of HW, located at v near 150 cm-1 and stipulated by harmonic longitudinal vibration of HB molecules, substantially exceeds such a peak of OW, since the elastic dipole moment / (D20) 8.8 D exceeds the moment / (H20) 3.5 D. 

The dielectric response shown in Fig. 43a resembles a highly damped resonance curve with the peak frequency v m located in the THz region. The s// L(v) spectra in Fig. 43b are compared for y =2.8 (curve 1) andy L = 2 (curve 2), for which the lifetimes t are respectively 0.089 and 0.14 ps. For greater y L (i.e., for shorter lifetime t l) the absorption curves become shallower. The frequency vj m of the loss-peak intensity, marked in Fig. 43b by the vertical lines, agrees with the estimate (193) only approximately. It is worthwhile to emphasize the following ... 

The real permittivity, at any temperature above of each polymer, as well as the intensity of the dielectric loss peaks observed for the main a-relaxation has been reported to be always greater for poly(AN-co-ATRIF) copolymer than for... 

The present dielectric results show that for corresponding frequencies the temperatures of the y loss maxima for pure PPO and PS are extremely close. At 100 Hz, for example, these occur at —116° and —119°C, respectively. Further, the temperature but not intensity of the PPO y peak is somewhat sensitive to sample preparation and could be shifted upwards by 5°-10° by increasing the annealing temperature from 180° to 210 °C. Even though annealing was conducted in vacuo, this indicates the possibility of the y peaks arising at least in part from polar species introduced as a result of oxidation. As has already been observed, the dynamic mechanical y loss peaks are uniformly weak, but as far as can be observed, the peak temperatures again are consistent with the dielectric data. 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

An enhanced dielectric loss maximum was observed at -85°C when a polysulfone sample which contained 0.76 wt. % unassociated water and no detectable level of clustered water (<0.01 wt. %) was run (Fig. 6, curve A). An apparent low temperature broadening of the dielectric loss dispersion was noted for another polysulfone specimen with 0.76 wt. % unassociated water and an additional 0.04 wt. % clustered water (Fig. 6, curve B). However, when a polysulfone sample which contained the same amount of unassociated water as the two prior samples but had 0.16 wt. % clustered water was analyzed, it had a significantly more intense loss peak centered near -105°C (Fig. 6, curve C). We believe that this shift in loss maximum and increase in loss intensity is caused by the development of an additional secondary loss peak about 20° below the 3-transition (Figure 6). In earlier work we had observed the same phenomenon in polycarbonate where the new loss peak occurred about 40 below its 3-transition as a separate loss peak. 

The dielectric loss behavior of PVAc was similar to that of the other polymers. An Increase in dielectric Intensity of the polymer s S mechanism was directly proportional to the amount of unclustered water. In addition when clustered water was present two separate low temperature peaks occurred as shown In the frequency dependent data of Figure 8. The higher frequency peaks were the result of clustered water. This is confirmed by the similarity between poly(vinyl acetate) and the clustered water peaks of other polymers as plotted in Figure 7. 

The dielectric strength. As, which is proportional to the area under the loss peak, is much lower for the secondary processes, relative to the a relaxation analysed in the next section. This is a common pattern foimd in both polymer materials and glass formers. The P secondary process is even more depleted in linear polymers that contain the dipole moment rigidly attached to the m chmn, such as polycarbonate [78-80] and poly(vinyl chloride) (the behaviour of this polymer was revisited in ref [81] where the secondary relaxation motions are considered as precursors of the a-relaxation motions). Polymers with flexible polar side-groups, like poly(n-alkyl methacrylate)s, constitute a special class where the P relaxation is rather intense due to some coupling vnth main chain motions. 

Thus, from both the DSC and the dielectric relaxation data cited earlier, the crossover of r y of PI in the HAPB of 35% and 20% PI with PtBS from VFT to Arrhenius dependences is not found at any temperature. This is the most direct proof that the confinement scenario is unreal. Arrese-lgor et al. (2010) admitted that the crossover predicted by the confinement scenario is not observed on Xaf of PI in the HAPB, but still maintained a vestige of confined dynamics by invoking the marked decrease of the intensity and increase of width as temperature decreases of the a-loss peak of PI in the 20% PI blend. 

Figure 5. Dielectric loss tan8 as a function of temperature at IkHz for poly(propylene oxide) in the imaged (o) and aged ( ) states. The aged sample was held for 5 hr at 5.3 C below Tg. Inset shows the tan8 peak intensity for the P relaxation as a function of aging time at 10.3 C below Tg. (Adapted from ref. 49.)...

The value of 13 versus temperature parallels the specific volume versus temperature and a change in slope can be observed in the range of the glass transition temperature. Another variable, I3, the oPs intensity(%) also varies with temperature and exhibits transitions (peaks) as a function of temperature with similarities to e" (dielectric loss) and E" (loss modulus) data. The fractional free volume (%) can be determined from [390]... 

Figures 3-5 that the dielectric relaxation again reveals only a single a relaxation for the mixtures. These are, however, noticeably broader than the a relaxation of the pure polymers. The temperatures of the loss maxima, when plotted (Figure 7) as a function of wu the weight fraction of PPO in the mixtures, do not display the smooth monotonic increase in T0 vs. Wi that was shown by both the Vibron and the DSC results. Instead, there is a pronounced increase in Tg above = 0.5 to give a sigmoid curve for this relation. Some reservations should be attached to this observation inasmuch as data for only three polyblend compositions are available nevertheless a qualitatively similar phenomenon is observed in the analysis of the intensity of the y peak (below). Further, if only the stronger maxima in the dynamical mechanical data are considered— i.e.y if the secondary peaks and shoulders which led to the identification of two phases are omitted—then a similar sigmoid curve is found. The significance of this observation is discussed later.

Various model available to fit the non-Debye relaxation profiles Width of loss pe also provide the measure of dynmnic heterc eneity Dielectric intensity/strength or a-peak decreases as crystallization progresses with time) Exact identity of molecular relaxor needs complementary analysis... 

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