Unoriented sample

For instance, in the three crystalline forms (a, 3, y) of i-PP the chains are always in the conformation of threefold helix (s(3/l)l symmetry) but are packed in different ways in monoclinic [24], hexagonal [25], and orthorhombic [26] unit cells, respectively. The X-ray diffraction spectra of unoriented samples in the crystalline forms a, P, y are reported in Fig. 6. 

Fig. 6 a-c. X-ray diffraction spectra (CuKa) of unoriented samples of a) a form b) y form c) p form containing only minor a form impurities [41]... 

In practice, commercially fabricated polymer items are generally oriented to some degree. The scattering patterns from such materials comprise arcs, which are parts of the full circles obtained from unoriented samples. The lengths and positions of these arcs reveal much about the orientation of crystallites within a sample. The shorter the arcs, the more oriented the sample. In cases of extreme orientation, as found in highly oriented fibers such as Kevlar , the scattering pattern can approach that of a single crystal. 

Fig. 13a-c. EPR spectra of Cu(TPP) diluted into a frozen nematic glass at 10 K (Merck Phase 5). a) Unoriented sample, b) Frozen nematic glass, oriented along B0 (B0 in the complex C plane), c) Frozen nematic glass, rotated by 90°. (Ref. [84])... 

The analysis of a full tilt series of 2H NMR spectra not only allows the determination of the unique bond angle for a deuteriated methyl group, but also provides an internal check for the consistency of the spectral interpretation. In particular, simulations provide a means for the analysis of line-broadening effects, which arise from the sample mosaic spread as well as the intrinsic line width of the nuclear transition and instrumental factors. When line shapes are fitted to a full tilt series of spectra in a concerted manner and are also compared with the powder spectrum of an unoriented sample, the different contributions can be discerned. In that way an intrinsic line width of around 2 kHz is found for the spectra shown here, together with a mosaic spread between 8° and 10° for the three samples. 

The simple water charmel models can explain the ionomer peak and the small-angle upturn in the scattering data of fhe unoriented samples as well as of the oriented films. Interestingly, the helical structure of backbone segments is responsible for fhe sfabilify of fhe long cylindrical charmels. The self-diffusion behavior of wafer and protons in Nation is well described by the water channel model. The existence of parallel wide channels af high wafer uptake favors large hydrodynamic confributions to electro-osmotic water transport and hydraulic permeation. 

Polarization Properties. One of Ae key attractions of XAS for biological systems is Ae ability to study unoriented samples such as protems in solution. If samples can be oriented, however, it is possible to greatly enhance Ae information content of XAS spectra. In particular, it is possible to obtain direct information about Ae relative orientation of specific structural features. These experiments are possible because the synchrotron X-ray beam is highly plane polarized. Several examples of polarized XAS of biologicA samples are Ascussed below. 

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. 

A / is the absorbance of the sample when the light is polarized parallel to a reference axis, and Aj is the absorbance of light which is polarized perpendicular to this axis. The strength of the absorption depends on the orientation of the electric field vector of the light and the transition moment of the chromophore - parallel orientation results in maximum absorption whereas perpendicular orientation leads to zero absorption. By dividing the LD value by the absorbance of the unoriented sample under isotropic conditions (Aiso), the reduced linear dichroism (LDr), i.e. the wavelength-dependent LD, is obtained (Eq. 7) [36]. 

The effects of morphology (i.e., crystallization rate) (6,7, 8) on the mechanical properties of semicrystalline polymers has been studied without observation of a transition from ductile to brittle failure behavior in unoriented samples of similar crystallinity. Often variations in ductlity are observed as spherulite size is varied, but this is normally confounded with sizable changes in percent crystallinity. This report demonstrates that a semicrystalline polymer, poly(hexamethylene sebacate) (HMS) may exhibit either ductile or brittle behavior dependent upon thermal history in a manner not directly related to volume relaxation or percent crystallinity. 

Studies were performed also with unoriented polyethylene terephthalate (Eisner, Koch, Bordas and Zachmann Also with unoriented samples the long period decreased with increasing time. Such a decrease has been observed already with samples quenched to room temperature (Zachmann and Schmidt The present results show that the decrease is not an artificial effect caused by quenching, but... 

By means of synchrotron radiation it is also possible to follow melting under isothermal conditions. Such experiments were performed on Polyethyleneterephtha-late. It was shown that with oriented samples melting occured more slowly and at higher temperatures than with unoriented samples. This is in agreement with the explanation of superheating effects by means of entropy considerations. 

Fig. 11. Nominal stress, CTj, versus extension ratio, for polycarbonate with different values of pre-orientation given by Anj. Samples drawn parallel to the orientation axis Ani = 0.029 (I), Ani = 0.016 (II) unoriented sample Ani = 0 (III) sample drawn perpendicular to the orientation axis Ani =0.017 (IV)...

A solid-state NMR technique for the determination of peptide backbone conformations at specific sites in unoriented samples under MAS has been described and demonstrated on labeled samples of tripeptide AlaClyGly and 17-residue peptide. Experiments and simulations show that both c ) and xj/ backbone dihedral angles can be extracted from a single data set. This technique, called DQCSA spectroscopy, may be especially useful when analyzing the backbone conformation of a polypeptide at a particular doubly labeled site in the presence of additional labeled carbons along the sequence. 

The X-ray diffraction of polymeric liquid crystal systems and their low mass counterparts are the same in principle, but the diffraction results for the polymers are often less ideal and more difficult to interpret. In practice the oriented specimens are often preferred over the unoriented samples for an unambiguous determination. X-ray diffraction is nearly always used together with texture observations using a polarizing optical microscope. Miscibility tests are also used in some cases for confirmation. For smectic phases with higher translational and orientational orders, X-ray diffraction is the most useful (if not the only) technique for unmistakable characterization. A few examples are cited below. The details of each characterization of the various polymeric smectic phases were described by individual authors. 

Orientation by cold drawing strongly affects the rate of alkaline hydrolysis. For unoriented samples, immersion of the sulfochlorinated films in 1 N NaOH for 24 hours at room temperature causes total hydrolysis, whereas 3 weeks are required to achieve it for some highly oriented samples of the same IEC. 

Since PVT measurements are conducted on unoriented samples, the three-dimensional percolation thresholds may be pertinent [Stauffer and Aharony, 1992 Ballesteros et al., 1999] ... 

Consequently, an expression for the orientation factor/can be obtained from Equations (5-22) and (5-12). /can be determined from the sound velocity in the fiber and in the unoriented sample ... 

Suppose that the light observed through the emission polarizer is completely polarized. Then /j = 0, and P-r = 1.0. This value can be observed for scattered light from an optic ly dilute scattered Completely polarized emission is never observed for fluorescence from homogeneous unoriented samples. The measured values of P ot r are smaller due to the angular dependence of photoselection (Section 10.2). Completely polarized emission can be observed for oriented samples. 

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