Wide-angle x-ray diffraction technique

Although it may be possible to measure this orientation using wide angle X-ray diffraction techniques, we present here only a qualitative comparison between the theory and experimental results. In Figure 10 we present the theoretical predictions of the shear stress at the start up of flow. We have assumed values of unity for... 

The determination of the atomic structure of crystalline polymers by wide angle X-ray diffraction techniques presents formidable problems which cannot conveniently be treated by the conventional methods of structure analysis. Consequently, existing methods need to be modified and new approaches to the problem developed to extract the maximum amount of structural information from the available experimental data. The nature of the problems encountered will be discussed in this paper, together with a description of methods that have been utilized to overcome them. A subsequent paper will deal with the applications of these methods to the determination of the molecular structure of several crystalline polyethers. 

X-ray Diffraction. The wide-angle x-ray diffraction technique (Fig. 6) is sensitive to the diffraction caused by crystalline regions. This technique is useful to obtain the orientation of a given direction of unit cell (generally a, b, and c axes). 

Fig. 6. Wide-angle x-ray diffraction technique, (a), (b) Flat film technique (c) diffractometer technique (111). Courtesy of John Wiley Sons, Inc...

Small-angle and wide-angle x-ray diffraction techniques have been reviewed in several articles and books [207-211]. 

The kinetics of transition from the liquid crystal to the fully ordered crystal of flexible, linear macromolecules was studied by Warner and Jaffe 38) on copolyesters of hydroxybenzoic acid, naphthalene dicarboxylic acid, isophthalic acid, and hydro-quinone. The analytical techniques were optical microscopy, calorimetry and wide angle X-ray diffraction. Despite the fact that massive structural rearrangements did not occur on crystallization, nucleation and growth followed the Avrami expression with an exponent of 2. The authors suggested a rod-like crystal growth. 

The above disadvantage of the lack of spatial information can be overcome by a combination of NMR data and other techniques. From the aH pulse NMR, the fraction and the molecular mobility of different molecular environment can be obtained as free induction decays (FIDs) within a short time, which is suitable for a practical, better understanding of the morphology-property relationship. Wide angle X-ray diffraction (WAXD) and small angle X-ray diffraction (SAXD) as well as electron microscopy provide direct information between the nano- and micrometre scale. A combination of NMR data with those from X-ray diffraction and electron microscopy should be able to analyse the structure from the atomic level to the macro scale. In this review, the morphology-property relationship, the dynamics of morphological transition, the kinetics of crystallisation, etc. analysed by a combination of NMR and other tools are introduced. 

X-ray diffraction tests are based on the fact that incident X-ray radiation is diffracted at certain angles by regularly spaced inclusions. The two main techniques used in reactive polymer systems are wide-angle X-ray diffraction (WAXD) and small-angle x-ray... 

The technique of wide angle X-ray diffraction is one of the most commonly used methods to determine crystalline orientation in polymeric materials. However, it is somewhat limited to polymeric materials whose crystallinity is generally greater than ten percent. What is... 

Wide angle X-ray diffraction is another technique which has been of vital importance in the understanding of oriented polymers. In this section we shall illustrate the usefulness of the X-ray method for characterising the crystalline orientation in polymers. It is intended that the discussion will be mostly descriptive, and the reader who wishes a review of the principles of measuring the intensity of diffracted X-ray radiation is referred to Refs. 32-34. 

In both cases ex-situ characterization experiments were carried out to probe the resulting structure, using techniques like density measurements and Wide Angle X-ray Diffraction (WAXD) patterns. The cooling mechanism and the temperature distribution across the sample thickness were analysed. Results show that the final structure is determined only by the imposed thermal history and pressure. 

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