Figure 2 Dielectric loss as a function of frequency for systems permitting chemically induced dielectric relaxation d) Schematic curves |

Figure 4.3 Frequency-dependence of the imaginary (loss) part of the dielectric relaxation function for PDE at different temperatures. The lines are fits by the Cole-Davidson function, Eq. (4-2), with cu = 2nf and temperature-dependent exponent given in Fig. 4-4. (Reprinted from Physica, A201 318, Stickel et al. (1993), with kind permission from Elsevier Science - NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.) |

Here e( )) is the complex dielectric function, co) and e"(

The dielectric loss factors d of the pure polypropylene and the composites containing the lignocellulosic materials derived from hemp and flax are presented in Figs. 14 and 15 as a function of the temperature for the frequency of 1000 Hz. Pure polypropylene is known to exhibit two characteristic features (Kotek et al., 2005) a glass relaxation p>eak around 263 K and a high - temperature ( 323 K) shoulder associated with chain relaxation in the crystalline phase. These features cannot be detected by the Dielectric Relaxation [Pg.208]

The relaxation map of Fig. 55 shows the temperature dependence of the most probable relaxation times xa, xp, and xy of neat EPON828 obtained. The dielectric ot-loss peak of neat EPON828 was well-fitted by the one-sided Fourier transform of the KWW function with n = 0.47. It is temperature-independent near Tg and together with xa(I), the corresponding Tq(T) is calculated by Eq. (10). The calculated values of xo(7) at 7 256 and 259 K near Tg are [Pg.575]

As with the dynamic mechanical relaxations, it is also possible to check the dielectric behavior of the sample. In this case the thermal analysis is carried out measuring the dielectric constant, dissipation factor, loss index, and phase angle as a function of temperature and frequency. In order to see a dielectric effect, a dipole must be connected with the molecular motion. In this way dielectric relaxation may be more specific than DMA. A combination of DMA, dielectric measurements, and DSC is often needed for a detailed interpretation of the properties of the materials. [Pg.362]

Figure 2 includes curves for and " calculated using equation 4 and the KWW function for = 0.50. The loss curve is broad and nonssrmmetrical, with a total half-width A1/2 2.2 (cf 1.14 for the SRT process). The dielectric data for glycerol conform approximately to the KWW function (fi increases from about 0.6 to 0.95 as temperature is increased). Thus dielectric relaxation in polymers and other materials is characterized by the shapes of the b and b" curves in addition to Ab and (t). [Pg.2230]

The accessibihty of chitin, mono-O-acetylchitin, and di-O-acetylchitin to lysozyme, as determined by the weight loss as a function of time, has been found to increase in the order chitin < mono-O-acetylchitin < di-O-acetylchitin [120]. The molecular motion and dielectric relaxation behavior of chitin and 0-acetyl-, 0-butyryl-, 0-hexanoyl and 0-decanoylchitin have been studied [121,122]. Chitin and 0-acetylchitin showed only one peak in the plot of the temperature dependence of the loss permittivity, whereas those derivatives having longer 0-acyl groups showed two peaks. [Pg.164]

In the previous subsection, we have provided conceptually the rationale and experimentally some data to justify the expectation that the primitive relaxation time To of the CM should correspond to the characteristic relaxation time of the Johari-Go Id stein (JG) secondary relaxation Xjg- Furthermore, it is clear from the CM relation, Ta = ( "to)1 1- , given before by Eq. 6 that To mimics Ta in behavior or vice versa. Thus, the same is expected to hold between Xjg and Ta. This expectation is confirmed in Section V from the properties of tjg- The JG relaxation exists in many glass-formers and hence there are plenty of experimental data to test the prediction, xjG T,P) xo(T,P). Broadband dielectric relaxation data collected over many decades of frequencies are best for carrying out the test. The fit of the a-loss peak by the one-sided Fourier transform of a Kohlrausch function [Eq. (1)] determines n and Ta, and together with tc 2 ps, To is calculated from Eq. 6 [Pg.551]

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