Mechanical and dielectric measurements

Transitions. Samples containing 50 mol % tetrafluoroethylene with ca 92% alternation were quenched in ice water or cooled slowly from the melt to minimise or maximize crystallinity, respectively (19). Internal motions were studied by dynamic mechanical and dielectric measurements, and by nuclear magnetic resonance. The dynamic mechanical behavior showed that the CC relaxation occurs at 110°C in the quenched sample in the slowly cooled sample it is shifted to 135°C. The P relaxation appears near —25°C. The y relaxation at — 120°C in the quenched sample is reduced in peak height in the slowly cooled sample and shifted to a slightly higher temperature. The CC and y relaxations reflect motions in the amorphous regions, whereas the P relaxation occurs in the crystalline regions. The y relaxation at — 120°C in dynamic mechanical measurements at 1 H2 appears at —35°C in dielectric measurements at 10 H2. The temperature of the CC relaxation varies from 145°C at 100 H2 to 170°C at 10 H2. In the mechanical measurement, it is 110°C. There is no evidence for relaxation in the dielectric data. 

Data from mechanical and dielectric measurements can be related in a qualitative, if not quantitative, manner. Formally, the dielectric constant can be regarded as the equivalent of the mechanical compliance. This highlights the fact that the dynamic... 

A great number of dynamic mechanical and dielectric measurements have supplied sufficient evidence that t0 may be regarded as a constant virtually independent of the temperature of measurement and of the polymer composition. If simplifying assumptions AS = 0 and AV = 0 are made, the Arrhenius equation is obtained... 

Table 1 Activation energies for the p transition peak in PET and PET/additive from mechanical and dielectric measurements...

The 13 C powder NMR line shapes of the carboxyl group chemical shift tensor are shown Fig. 115 as a function of temperature. At 27 °C, a nearly regular powder spectrum is found, with o = 268 ppm, <722 = 150 ppm and (733 = 112 ppm. As temperature rises, increasingly pronounced line-shape changes are observed, which are indicative of large motions with rates exceeding 10 kHz. The motional rates estimated at the various temperatures fit quite well on the relaxation map of PMMA obtained from mechanical and dielectric measurements (Fig. 111). Thus, the motions of the carboxyl groups observed by NMR are directly related to the f3 transition. 

The investigation reported in this paper shows that, in spite of the detailed information provided by solid-state NMR or atomistic modelling, combination with mechanical and dielectric measurements is necessary. 

The characterization of solid polymeric material often includes the need to characterize the variety of molecular motions present as well as the molecular and morphological structure. NMR relaxation measurements have a long history of application to molecular motion studies of polymers where NMR data often complements mechanical and dielectric measurements with a more complete identification of the mobile, or immobile, entities. 

Figure 5.5. State diagram of sucrose with typical experimental data at high concentrations and in the maximally freeze-concentrated state. Dynamic mechanical and dielectric measurements show glass transition-related relaxations.

The lowest temperature 6 peak appears at approximately -160 C in the vibrating reed measurement whereas only the onset of 6 relaxation can be seen near -18O C in the torsional pendulum test. As discussed below, this peak is not present in the Nafion acid or in its salt membranes in both mechanical and dielectric measurements. 

The hydrogenated, sulfonated PP s were compression molded into films suitable for differential scanning calorimetry (DSC), dynamic mechanical, and dielectric measurements. Films were prepared by preheating at 140°-145°C for 5 min and then pressing at 140°—145°C and 20,000 lb for 5 min. Annealed samples were prepared by placing aircooled films between two metal platens and storing them in a vacuum oven at 80 °C for 3 days. The platens were necessary to prevent the films... 

Data from mechanical and dielectric measurements can be related, certainly in a qualitative, if not always in a quantitative, way. Formally, the dielectric constant (e ) can be regarded as the equivalent of the mechanical compliance (J ), rather than the modulus, and this highlights the fact that mechanical techniques measure the ability of the system to resist movement, whereas the dielectric approach is a measurement of the ability of the system to move, given that the groups involved must also be dipolar. Interestingly, the dielectric loss (e") appears to match the loss modulus E" or G") more closely than the loss compliance when data are compared for the same system. 

Kimmel and Andrews [195] have summarized measurements of the PAN Tg, up to the year 1965. The values fall into two ranges. For static measurements, distinct changes in the temperature dependence of the measured property are observed around 85 95°C. Higher values of Tg, 105 140°C, are obtained using dynamic mechanical and dielectric measurements, Tg values of 85 and 87°C, based on the linear expansion coefficient, were reported by Bohn et al. [120] and Howard [196]. Howard determined the Tg for a series of (AN-VA) copolymers by measuring the linear expansion coefficient of copolymer discs. The Tg for the PAN homopolymer was determined to be 87°C. Upon incorporation of VA, the value of Tg... 

Dynamic-mechanical and dielectric data have been widely reported for most aliphatic polyamides, especially poly(g-caprolactam) (nylon-6 or PA-6 rg 313K) and poly(hexamethylene adipamide) (nylon-6,6 or PA-6,6 Tg 323 K). Results of dynamic-mechanical and dielectric measurements of PA-6 and PA-6,6 (Table 13.8) provide evidence for three relaxations (/3, y, and 8) in these polymers at temperatures below their crystalline-melting temperature Tni (487-506 K for PA-6 and 523-545 K for PA-6,6) [8]. The /3 relaxation (located at above 310-347 K for PA-6,6 and 357-370 K for PA-6,6) is associated with high... 

Johannsmann D. Viscoelastic, mechanical, and dielectric measurements on complex samples with the quartz crystal microbalance. Phys Chem Chem Phys 2008 10(31) 4516-4534. 

Johannsmann D (2008) Viscoelastic, mechanical, and dielectrical measurements on complex samples with the quartz crystal microbalance. Phys Chem Chem Phys 10 4516-4534 Konig AM, Diiwel M, Du B, Kunze M, Johannsmann D (2006) Measurements of inteifacial viscoelasticity with a quartz laystal microbalance influence of acoustic scathaing from a small crystal-sample contact Langmuir 22 229-233... 

Two principal approaches have been used to model the yield behaviour of polymers. The first approach addresses the temperature and strain-rate dependence of the yield stress in terms of the Eyring equation for thermally activated processes [39]. This approach has been applied to many amorphous and crystalline polymers (see Section 12.5.1) and links have been established with molecular relaxation processes determined by dynamic mechanical and dielectric measurements and with non-linear viscoelastic behaviour determined by creep and stress relaxation. The Eyring approach assumes that the yield process is velocity controlled, i.e. the yield process relates to existing thermally activated processes that are accelerated by the application of the yield stress to the point where the rate of plastic deformation reaches the applied macroscopic strain rate. This approach has... 

The glass transition temperature for polymer blends often shows broadening (broader relaxation spectra for dynamic mechanical and dielectric measurements and broader transitions for calorimetric measurements). These observation are generally observed for borderline misci-... 

However, it can be shown that tan is analogous to tan Se (5). Examples of mechanical and dielectric measurements are given in Figure 1. 

In alkyl-substituted methacrylate polymers, an additional transition is detected ultrasonically and has also been observed using dynamic mechanical and dielectric measurements. This relaxation is associated with conformational changes of the alkane side chain (Figure 17). The motion of... 

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