Unoriented crystal fraction

The total crystal fraction, oriented crystal fraction (/oc). and unoriented crystal fraction (/uc) during extension and retraction have been analyzed. Results can be described as follows. At strain zero, the total crystal fraction was the same as the unoriented crystal fraction, which was about 14%, and both values decreased with strain. This indicates that a fraction of the original crystals was destroyed at the initial deformation stages. (This phenomenon was also reported in ethylene-based ethylene-propylene copolymer (34).) At strain 0.7, the total crystal fraction decreased about 4% (from 14% to 10%) at strains above 0.7, both total crystal fraction and oriented crystal fraction increased with strain, indicating the occurrence of strain-induced crystallization, whereas the unoriented crystal fraction decreased continuously with strain. The increase of the total crystal fraction was slower than that of the oriented crystal fraction, suggesting that some unoriented crystals were reoriented by... 

A very remarkable deconvolution procedure, schematized in Figure 21.3, has been proposed, by which it is possible to extract additional structural information i.e., fractions of oriented crystal, unoriented crystal, oriented amorphous, and unoriented amorphous phases) besides conventional data such as crystal unit cell parameters and crystal size. 

In diffraction patterns made from unoriented samples, the crystalline pattern is superimposed on an amorphous halo. As shown in Fig. 5, the percentage of amorphous material may be calculated by comparing the intensities of the two portions of the diffraction pattern. When the amorphous fraction is large, as in samples which have been quenched rapidly from the melt to a low temperature, the crystal structure may be greatly disrupted. Various interpretations of the intermolecular and intramolecular order which may be deduced from the diffraction patterns of such samples are discussed by Kilian and Jenckel. 

This deconvolution of the contributions due to the oriented and unoriented polymer allowed to show that, during the stretching of NR, only a small fraction of the amorphous chains become oriented and subsequently crystallize, while the majority of amorphous chains remain unstretched even at very large strains. The presence of cross-links is the main reason why chains are recalcitrant to rearranging and realigning according to the stress imposed. ... 

It has also been noticed that within some temperature interval around the transition points and NI the two neighbouring phases are not strictly homogeneous, but each phase contains embryos of the other phase. The relative amount of the phase existing in an embryonic form remains very small up to temperatures very close to the transition point, but it is detectable by NMR. Figure 1 shows several proton NMR spectra of DDA9-L representative of (A) the isotropic phase with a small nematic fraction, (B) nematic phase with a small isotropic fraction (1-2 %), (C) pure nematic phase homogeneously oriented, (D) unoriented nematic phase, or solid phase above the cold crystallization temperature, (E) solid phase with some nematic fraction, and (F) solid phase near room temperature. It is interesting to note that the sharp peak at the centre of spectrum B, which could not be obtained in the line shape simulation procedure reported in... 

This polymer is of special interest due to its commercial importance as an electroactive material e.g. as piezo- or pyro-electric films). The molecule is highly polar and the material may exist in five crystal forms in three of which the molecular dipoles are parallel.It is evident from a study of the early literature (see ref. 10 for a review) that the dielectric behaviour of this polymer is the most complex of all the linear polymer systems. Studies have been made for partially crystalline samples having different crystal forms, different degrees of orientation and crystallinity, and electrical and thermal histories. Unoriented materials may have degrees of crystallinity up to 50% so they are composites of crystalline and amorphous regions with the attendant complications of relating the measured permittivities to the volume fractions of the phases, the permittivities of the phases, including and for the crystals, and the orientation distribution function of the crystallites, as has... 

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