Crystalline relaxation

Dynamic mechanical measurements were made on PTEE samples saturated with various halocarbons (88). The peaks in loss modulus associated with the amorphous relaxation near —90°C and the crystalline relaxation near room temperature were not affected by these additives. An additional loss peak appeared near —30° C, and the modulus was reduced at all higher temperatures. The amorphous relaxation that appears as a peak in the loss compliance at 134°C is shifted to 45—70°C in the swollen samples. 

EVALUATION OF MELTING AND CRYSTALLINE RELAXATION TEMPERATURES OF FATTY ACID MONOLAYERS ON THE WATER SURFACE... 

Table 1. Melting temperature, Tm, and crystalline relaxation temperature, Tctc> of fatty acid monolayers on the water surface. 

A) The crystallite of the polymer itself exhibits a relaxational character (crystalline relaxation). 

The temperature dependence of e and k in a roll-drawn and polarized PVDF was measured by Oshiki and Fukada (1971) and is illustrated in Fig. 28. Both quantities have maxima at — 20° C and 50° C where dielectric loss peaks are observed, due to primary and crystalline relaxations, respectively (Sasabe and others, 1969). 

Changes in the amorphous relaxation behaviour with rising temperature exhibited a monotonous reduction of the integral width, independent of sample morphology, while a crystalline relaxation change is unique for each sample. Thus, the complete analysis of XH FID allows us to discuss chain mobility of amorphous and crystalline phase independently. 

A widely used interpretation of the compensation law is based on a two-site model proposed by Hoffman et al. (22) to describe crystalline relaxations in n-paraffins. Molecular movements are assumed to involve an entire short-chain molecule, the length of the molecules corresponding to the thickness of crystallites. Under these assumptions, the relaxation time is expressed by an Eyring equation (Equation 1E9), with... 

The subscripts eg and cs refer to end-group contribution and to elementary contribution of constitutive segments, respectively, and n is the number of segments per molecular chain. This model was applied satisfactorily to n-paraffins, but also to n-esters and n-ether. A linear variation of both the activation enthalpy and entropy as a function of n has been observed experimentally (22). One may designate as 7 the parameter that joins the intrinsic components describing the elementary contributions of the crystalline relaxation, i.e.,... 

It is seen that E for undrawn PVA film shows broad and sharp peaks around -35°C and 30°C, respectively, which are termed as the y and P peaks, respectively. Similar peaks appearing below 0°C were observed by Nishio et al. (1988), and in their study, other peaks located at about 80°C and 35°C were reported as the dispersions due to relaxations in the amorphous PVA regions, and the dispersions observed above 100°C were due to the crystalline relaxations of PVA. 

The a transition is associated with crystalline relaxations occurring below the melting point of PE. 

Figure 8.8 Schematic representations of change in modulus E with temperature on the Takayanagi model for (a) the and (h) the L situations corresponding to Eo and 90, respectively. Calculations assume amorphous relaxation at temperature r(aa) and crystalline relaxation at temperature r( c) and (c) shows combined results. C, crystalline phase A, amorphous phase. (Reproduced with permission from Takayanagi, Imada and Kajiyama, J. Polym. Sci. C, 15, 263 (1966).

In semicrystalline polymers the a relaxation is not always the glass transition of the amorphous phase often it is a crystalline relaxation (also denoted as the relaxation). In sueh cases, the glass transition is usually denoted as the P or a, relaxation. 

Although a detailed analysis has been given for the polyethylenes, because of the extensive amoimt of experimental data that is available, a similar basis for the P transition also exists in other crystalline polymers. The dynamic-mechanical behavior of poly(oxymethylene) is in fact very similar to that of polyethylene. This polymer displays a crystalline relaxation and two others, which are usually referred to as the P and y relaxations. The introduction of small amounts of ethylene oxide co-vmits into the chain greatly enhances the intensity of the originally weak p transition. These results parallel those for copolymers of ethylene and indicate that they have a common origin. Since the ethylene oxide co-units are effectively excluded from the crystal lattice, an enhanced interfacial stmcture would be expected. 

Seguela et al. [170] proposed that the driving force for the nucleation and propagation of screw dislocations across the crystal width relies on chain twist defects that migrate along the chain stems and allow a step>-by-step translation of the stems through the crystal thickness. The motion of such thermally activated defects is responsible for a crystalline relaxation. 

Blending with PMMA almost does not affect the locations of all these relaxations on the temperature or frequency scale, respectively (Fig. 4 (S6-60.72.73]). IMth respect to the a a 7 relaxations, ihn is in accordance with the proposed molecular origins, since crystalline relaxations cannot be influenced by Mending. The relaxation, however, should change evenly with temperature after addition of PMMA between the f/s of the components (7,(PVDF) —40 7,(PMMA) " IKTC] if it is really doe to the glass... 

Figure 8.3 illustrates the FID fitted with two amorphous and one crystalline relaxation components for an MGC. The fitting is carried out by the following procedure. First, the longest relaxation was fitted in the time region of 200-400 ps. After subhaction of the first component from FID, the residual plots were further fitted by another amorphous component. The resultant crystalline relaxation is well represented by Equation 8.5. The sum of these curves is in perfect agreement with the observed FID, as shown in Figure 8.3. 

The positions of troughs are a good measure of the state of the crystalline and amorphous phases. The unchanged position of the first trough around 19 ps in Figure 8.10, which is independent of prior polymer concentration, means the constant level of crystalline relaxation. The position of the... 

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