Quenched samples

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. 

The melting point of commercial Teflon PEA is 305°C, ie, between those of PTEE and EEP. Second-order transitions are at —100, —30, and 90°C, as determined by a torsion pendulum (21). The crystallinity of the virgin resin is 65—75%. Specific gravity and crystallinity increase as the cooling rate is reduced. An ice-quenched sample with 48% crystallinity has a specific gravity of 2.123, whereas the press-cooled sample has a crystallinity of 58% and a specific gravity of 2.157. 

The x-ray diffractograms of those three samples are shown in Fig. 12. The lower pattern corresponds to the quenched sample where only the mesophase is present (the layer line, appearing at lower angles is not shown). The other two diagrams corresponding to the annealed samples present several sharp diffraction peaks, which... 

In Fig. 5.1, the densities of the annealed and of the quenched polymers are plotted against Mh the inverse molecular mass of the network strands. All the annealed samples were denser by about 0.15% than the quenched ones. Bero and Plazek [52] observed an effect of similar magnitude between quenched samples and samples cooled at 0.2 K/h. 

Fig. 5.3. Young s moduli Efle, as determined by flexural tests on small samples after thermal treatment are plotted against the densities of those samples. The dots are situated along a single line since the annealed samples are denser and more rigid than the quenched samples prepared from the same polymer...

Model Deyelopment. Rachow and Timm (] ) derived working relationships for the kinetic mechanism described. Degree of polymerization is considered to be a continuous variable. For quenched samples a relationship correlating population density of associated polymer molecules as a function of time, degree of polymerization and environmental factors is... 

The kinetic mechanism subject to quenched samples requires that each polymer molecule formed will contain one butyl residue... 

Secondary crystallization occurs most readily in polymers that have been quench-cooled. Quenched samples have low degrees of crystallinity and thus have relatively large volumes of amorphous material. A pre-requisite for secondary crystallization is that the amorphous regions must be in the rubbery amorphous state. Increased temperature accelerates the rate of secondary crystallization. The new volumes of crystallinity that form during secondary crystallization are generally quite small, amounting to less than 10% of the crystalline volume created during primary crystallization. 

Figure 16 Typical electron micrographs of quenched samples of indicated molecular weight fractions of linear polyethylene. Reproduced with permission from Ref. [231]. Copyright 1984, John Wiley 8t Sons, Inc.

Fig. 5 Difference intensity SAXS curves of PET after subtraction of the intensity of the melt-quench sample crystallized from the glassy state at 80 C for 3-122 min (a) and 157-313 min (b) [7]...

Sample Preparation. Samples for mechanical studies were made by compression molding the polymers at 150°C between Teflon sheets for 15 minutes followed by rapid quenching to room temperature in air. These will be referred to as PQ (press-quenched or simply quenched) samples. The thickness of the PQ samples was around 10 mils (0.25 mm). The thermal history of all of the PQ samples (HBIB, HIBI, and LDPE) were essentially the same. They were used within one week after they were pressed. Samples for morphology, SALS and SEM studies were prepared from toluene solutions. These films were cast on a Teflon sheet at 80 C from a 1% (by weight) solution in toluene. These films were about 5 mils in thickness. When the polymer films had solidified (after 5 hrs), they were stored in a vacuum oven at 80°C for two days to remove residual solvent. These samples will be designated by TOL (solution cast from toluene). 

The DSC thermograms of several triblock copolymers and homopolymer HB are coiq>ared to that of a low density polyethylene in Figure 2. The thermograms are those of the first run on quenched samples. Their behavior is similar except that the temperature of the maximum in the DSC melting peak, Tm, for LDPE (110 C) is higher than that of HB (102°C). The depression of the melting point brought about by the presence of 5 to 8 mole percent... 

Fig. 9 XRD of quenched samples of Sc MgjCu/ia r The v = 46.0 and 48.5 products are the 1/1 AC, that for y = 48.0 is the i-QC, and y = 47.0 results in a mixture of the QC and Sc2CuGa3. The inset and the six integers show the ED pattern of the i-QC along a fivefold axis and the sixdimensional indices. (Reproduced with permission from [79]. Copyright 2005 American Chemical Society)...

Fig. 17 Section of Ca-Au Ga phase diagram showing the distribution of 1/0, 1/1, 2/1 ACs in samples that were slowly cooled from 800°C and annealed at 500°C. Note that the i-QC is obtained only in quenched samples near CaAujGaj (marked by the arrow)...

Measurement of the amount of tritium in the quenched samples was made by reheating them in a normal hydrogen ambient and measuring the evolved radioactivity. Since the samples contained tritium not only dissolved in the bulk crystal but also attached to the surface, mainly in a thin oxide film, measurements were made with and without removal of the latter by etching with HF, a procedure verified to remove the surface radioactivity. Their final results for the solubility s fell nicely on the Arrhenius line, ... 

In order to investigate the competition between magnetic interaction and spin transition in (bpym, S), quenching experiments have been performed at 0.63 GPa. Fig. 7 displays the magnetic behaviour of the quenched sample at increasing temperatures. It can be inferred from the thermal dependence of XmT that [HS-HS] entities can be frozen-in as a metastable state at low temperatures. Heating the sample above ca. 60 K leads to re-formation of... 

A fTiCr2 (Ni2Mg type, —65-66 at.% Cr) form has also been described either as a high temperature phase (stable from 1270°C up to the melting point, 1370°C) or, probably, as a metastable phase occurring only in quenched samples. 

J. R. Lakowicz, H. Cherek, I. Gryczynski, N. Joshi, and M. L. Johnson, Enhanced resolution of fluorescence anisotropy decays by simultaneous analysis of progressively quenched samples, Biophys. J. 51, 755-768 (1987). 

Using contrast matching methods of SANS, Nafion was swollen with various mixtures of H2O and D2O in order to highlight the scattering features of the water swollen ionic domains. Furthermore, quenched samples were used in these studies to eliminate the scattering features attributed to the crystalline do-... 

Single crystal X-ray diffraction and neutron diffraction studies of a quenched sample indicated that the vacancies were not spread statistically over the structure, but were arranged in clusters (Koch/Cohen clusters) consisting of 13 vacancies and four... 

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