Segmental motion from dielectric relaxation

Poly(4-chloro styrene) P4CS 411.5 11.4 58.0 [62] ar,a for local segmental motion from dielectric relaxation data. 

Poly(vinyl methyl ether) PVME 244 14 42 250 [76] aT,a of local segmental motion from dielectric relaxation in the range 10 ° > > 10 s. 

Pn-BMA 373 8.5 185 300 [88] ar,a of local segmental motion from dielectric relaxation 10°[Pg.462]

Poly(cyclohexyl methacrylate) PCHMA M = 2x 10 Heterogeneous backbone polymers 359.7 14.8 75.67 374 [99] aj a of local segmental motion from data of local density fluctuation observed by PCS, mechanical relaxation and dielectric relaxation. When referenced to the respective TgS (I.e. plotting log(ar, ) against (T-Tg) the shift factor of PCHMA has a considerably stronger temperature dependence than that of Pn-HMA. 

Fig. 16 shows k and k for as-cast PVDF at frequencies from 1 kHz to 500 kHz (Hayakawa and Wada (2), 1971). The dielectric relaxation of the sample is illustrated in Fig. 17 for comparison. The observed relaxation is due to the segmental motion in the amorphous phase of PVDF (Sasabe and others, 1969). The curves of k have a maximum at a frequency similar to that of the e" maximum, indicating that as is negative and that the last term on the right-hand side erf Eq. (106) is more dominant than the first and second terms. This is also confirmed in the curves of k", which pass through zero at a frequency of maximum e" or k. ... 

The analysis of the real and imaginary part of the complex dielectric permittivity allows one to distinguish between the two main relaxation processes (a and P). The a-process is correlated to the transition from the ferro to the paraelectric phase and the p-process is attributed to segmental motions in the amorphous phase. 

Secondary relaxations are usually measured either by mechanical methods such as dynamic mechanical spectroscopy or (somewhat less often) by electrical methods such as dielectric relaxation spectroscopy [159], The existence of Tp is generally ascribed to the onset of a significant amount of some kind of motion of the polymer chains and/or the side groups attached to them, on a much smaller and more localized scale than the large-scale cooperative motions of chain segments associated with Ta. These motions are usually inferred from the results of measurements using methods such as nuclear magnetic resonance spectroscopy. See... 

Thus two dielectric relaxation processes, a segmental and a normal mode process, are present [5] they are well-separated on the frequency and temperamre scale (Fig. 21.9). The relaxation process around 220 K originates from a local segmental motion perpendicular to the main axis, while the second relaxation process at higher temperatures is assigned to fluctuations of the dipole components parallel to the chain contour (normal mode). 

PVE 271.3 12.0 36.8 [127] component resolved In the dielectric relaxation spectra (not thermorheologically simple). ar,a of local segmental motion of PVE from... 

Entanglements of flexible polymer chains contribute to non-linear viscoelastic response. Motions hindered by entanglements are a contributor to dielectric and diffusion properties since they constrain chain dynamics. Macromolecular dynamics are theoretically described by the reptation model. Reptation includes fluctuations in chain contour length, entanglement release, tube dilation, and retraction of side chains as the molecules translate using segmental motions, through a theoretical tube. The reptation model shows favourable comparison with experimental data from viscoelastic and dielectric measurements. The model reveals much about chain dynamics, relaxation times and molecular structures of individual macromolecules. 

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