Specimens, oriented

Fig. 2. (continued)—(d) an aggregate of microcrystallites whose long axes are parallel, but randomly oriented (left), diffracts to produce a series of layer lines (right) and (e) a polycrystalline and preferentially oriented specimen (left) diffracts to give Bragg reflections on layer lines (right). The meridional reflection on the fourth layer line indicates 4-fold helix symmetry. 

Polycrystalline and well-oriented specimens of pure amylose have been trapped both in the A- and B-forms of starch, and their diffraction patterns84-85 are suitable for detailed structure analysis. Further, amylose can be regenerated in the presence of solvents or complexed with such molecules as alcohols, fatty acids, and iodine the molecular structures and crystalline arrangements in these materials are classified under V-amylose. When amylose complexes with alkali or such salts as KBr, the resulting structures86 are surprisingly far from those of V-amyloses. 

When X = Y, as in polyethylene, poly-(tetrafluoroethylene), polyisobutylene, and poly -(vinylidene chloride), the polymers are highly crystalline products with sharply definable melting points (except for polyisobutylene, which crystallizes readily on stretching but with difficulty on cooling). Oriented specimens of high strength may be obtained, exactly as in the crystalline condensation polymers. 

Figure 4 is a set of contour plots of data derived from three Standard Pole Figure scans on a highly oriented specimen of linear polyethylene. The contour plotting software establishes a set of intensity levels that span the data in the diffraction data file. 

The small class of trumpet-shaped receptacles (figure 2b) is divided between Palenque and Plains orientations. Specimens relating to the latter have low probabilities of group containment (SPSS) and are unassigned to any reference unit by ADCORR. 

The structures of agarose, iota- and kappa-carrageenan have been determined by x-ray fiber diffraction (24-27). The quality of the diffraction data obtained from each of these three specimens varies considerably and the way in which these data are used in structure determination is outlined here. Diffraction patterns from oriented specimens of agarose, and kappa- and iota-carrageenan are shown in Figure 6 (28). The molecular repeat distances derived from these patterns are listed in Table I. 

The relative positions of a sufficient number of reflections arising from microstructural periodicities enable unambiguous identification of morphology. Further information can be obtained by preparing oriented specimens, and obtaining diffraction patterns for different orientations. For example, in an oriented lamellar phase with the beam incident parallel to the layers, Bragg... 

Crystallization in poly(ethy ene)-poly(ethylethylene) (PE-PEE) semicrystalline diblock copolymers has been investigated using SAXS and WAXS on oriented specimens. Microphase separation was found to precede crystallization for all samples, with 37-90wt% PE (Douzinas and Cohen 1992). The scaling of the lamellar domain spacing in the crystalline phase for the same samples was determined from measurements of the principal SAXS peak position (Douzinas et al. 1991). It was found that the domain spacing scales in agreement with the predictions of the theory of Whitmore and Noolandi (1988) (Section 5.3.5), i.e. 

It has been shown (Beer (72)] that under certain circumstances it is permissible to consider a polymer specimen as made up of a fraction,/, of fully oriented chains (i. e with molecular axis exactly parallel with the fiber axis) and the remainder, 1 — /, of randomly oriented chains. The necessary condition is satisfied by axially oriented polymers, regardless of the specific nature of the distribution of chains. A convenient relationship between /, the observed dichroic ratio R, and the dichroic ratio of perfectly oriented chains R0= is given as follows (Fraser (59)]. In an axially oriented specimen the extinction coefficient in a given direction for the unoriented portion is simply related to en and ea for the oriented portion. Since the total extinction coefficient for the latter is given by e - 2 F,a, the extinction coefficient for the unoriented portion in a given direction is... 

The spectrum of an oriented specimen of PVC is shown in Fig. 9. This specimen is a typical low-crystallinity PVC. Higher crystallinity specimens, prepared by polymerization at low temperatures [Grisenth-waite and Hunter 68) Krimm, Berens, Folt, and Shipman 105) ... 

The polarized infrared spectrum of an oriented specimen of PVA is shown in Fig. 11 [Krimm, Liang, and Sutherland (104)]. The band positions and polarization, given in Table 13, are derived from this and... 

Polarized infrared spectra of oriented specimens of isotactic polypropylene are shown in Fig. 14 [Peraldo (167)]. The band positions, polarizations, and relative intensities are given in Table 14, together with Raman data [Tobin 231)] and information on the phase of origin of the bands [Natta [149) Pokrovsky and Volken-shtein 178) Abe and Yanagisawa (/)]. Some preliminary data on partially deuterated polypropylenes are available [Peraldo 167) Natta 130)], but no detailed spectra have as yet been published. 

The infrared spectrum of a sample of atactic polystyrene is shown in Fig. 15 [Liang and Krimm (114)]. The band positions are given in Table 16, on the left-hand side of the "Infrared column. Raman data for atactic polystyrene [Signer and Weiler (198) Palm (163)] are also included in the table. Polarized spectra of oriented specimens of isotactic polystyrene have recently been published [Tadokoro, Nishiyama, Noza-kura, and Murahashi (227) Tadokoro, Nozakura, Kitazawa, Yasuhara, and Murahashi (222) Takeda, Iimura, Ya-mada, and Imamura (222a) Morero, Man-tica, Ciampelli, and Sianesi (140a)]. The spectrum of the isotactic polymer differs slightly from that of the atactic polymer, and these differences (above 500 cm-1) are shown... 

S. Seki, I. Nitta, and R. Yamadera X-ray and infrared-microspectro-scopic measurements on a highly double-oriented specimen of polyvinyl alcohol. J. Polymer Sci. 28, 244—247 (1958). 

Oriented"specimens. The least ordered situations we will... 

Figure 5. Diffraction from an uniaxially oriented specimen of stretched calf thymus DNA (courtesy M. H. F. Wilkins). The molecules are approximately 14, helices with c = 10.6 nm. The Bragg reflections on the equator can be indexed on the basis of a rhombic net with a = b = 2.30 nm.

A method is described which enables structural parameters of non-crystalline polymers to be determined. It is based on the analysis of wide-angle X-ray scattering and where possible incorporates the additional information obtainable from oriented specimens. Particular emphasis is placed on the analysis of the structure of molten polyethylene. The potential application of the approach to the structure of the amorphous phase in semicrystalline polymers is discussed. 

ASTM E 2405 Standard Test Method for Determination of Fire and Thermal Parameters of Materials Using an Intermediate Scale Test with Vertically Oriented Specimen... 

For textile materials used as interior wall-coverings in U.K. buildings including railway carriages, where the fabric could be in a vertical orientation attached to the wall panel, measurement of rate of flame spread under external heat flux is one of the requirements. For such applications, the test method (BS 476 Part 7) essentially requires a vertically oriented specimen exposed to gas-fired radiant panel with incident heat flux of 32.5kW/m2 for lOmin. In addition, a pilot flame is applied at the bottom corner of the specimen for 1 min 30 s and rate of flame spread is measured. The same principle is used in the French test for carpets, NF P 92-506. 

BS 5438 1989 British Standard Methods of test for flammability of textile fabrics when subjected to a small igniting flame apphed to the face or bottom edge of vertically oriented specimens. 

---