Orientation and crystallinity

The Emerman model described in the previous section is hardly applicable to the carbon black-filled CCM as the black particles have sizes of hundreds angstrom and such a composite, compared with the molding channel size, may be considered as a homogeneous viscous fluid. Therefore, the polymer structure, crystallinity and orientation play an important role for such small particles. The above-given example of manufacture of the CCM demonstrates the importance of these factors being considered during processing of a composite material to and article with the desired electrical properties. 

The fourth category represents the state when the specimen is both crystalline and oriented as in Fig. 2e, and it is the best scenario for successful structure analysis. Note that the individual crystallites are large, with sufficient lateral... 

Chemical structure Molecular weight Crystallinity and orientation Cross-linking Addition of other agents... 

The resulting CuInTe2 films are crystalline and oriented (Fig. 3.10a,b). The fringes in the cross-sectional TEM image of the film, which run parallel to the... 

Quantitative determination of the major and minor minerals In geological materials Is commonly attempted by x-ray diffraction (XRD) techniques. Mineralogists use a variety of sophisticated and often tedious procedures to obtain semlquantltatlve estimates of the minerals In a solid sample. The mineralogist knows that XRD Intensities depend on the quantity of each mineral component In the sample even through expressions for conversion of signal Intensity to quantitative analysis often are unknown or difficult to determine. Serious difficulties caused by variables such as particle size, crystallinity, and orientation make quantification of many sample types Impractical. Because of a lack of suitable standards, these difficulties are particularly manifest for clay minerals. Nevertheless, XRD remains the most generally used method for quan-... 

The single-crystal GaAs wafers are used as substrates for the growth of very thin layers of the same or other III-V compounds having the desired electronic or optical properties. Such crystal growth, in which the substrate determines the crystallinity and orientation of the grown layer, is called epitaxy, and a variety of epitaxial growth techniques are used in III-V display and device production. 

Raman spectroscopy is well suited for examining calcified tissues such as bones and teeth owing to its ability to probe both the inorganic and organic constituents of the tissue. The frequency and band shape of the symmetric and asymmetric phosphate stretching vibrations provide critical information on the crystallinity and orientation of the hydroxyapatite matrix. The analysis of a Raman spectrum of dental enamel provides features that are highly characteristic of the health and integrity of the tissue. 

Marchessault et at. (27) obtained weakly crystalline and oriented fibers(A) by extruding a 10% DMSO solution of crudlan into CH3OH at room temperature and washing it in water. They found that the same fiber annealed in water, under tension, at 140°C, in a sealed bomb, is of higher crystallinity and occured as two reversible crystalline polymorphs one at high relative humidity(B) and the other at humidities less than 20%(C). 

The simplest mechanical properties are those of homogeneous isotropic and purely elastic materials their mechanical response can be defined by only two constants, e.g. the Young modulus E and the Poisson ratio v. For anisotropic, oriented-amorphous, crystalline and oriented-crystalline materials more constants are required to describe the mechanical behaviour. 

The re-values calculated by means of the Molar Permachor are valid for amorphous polymers. For semi-crystalline and oriented polymer films a correction must be made. Salame recommends for semi-crystalline polymers the following expression ... 

All mechanical properties depend on crystallinity, orientation and crosslinking. These three factors will all be discussed in this chapter. See also Kinloch and Young [2] and van Krevclcn [71 for discussions on the effects of crystallinity and orientation on the mechanical properties. The discussion of the morphologies and the mechanical properties of multiphase polymeric systems (such as composites and blends) will be postponed to Chapter 19 and Chapter 20, respectively, where crystallinity and orientation will be discussed further in this broad context. 

For a given polymeric structure, the morphology (crystallinity and orientation), formulation (additives, fillers and impurities), humidity (especially for polar polymers), temperature, and pressure, are the most important factors which affect the thennal conductivity. References [1-8] review many of these factors. In addition, see Bigg [14] and Ross et al [15] for detailed treatments of the effects of fillers and of pressure, respectively, on thermal conductivity. 

X-ray diffraction techniques are the only way of determining the crystal structure of natural and synthetic polymers, although the x-ray data itself obtained from a crystalline polymeric fiber or film is not sufficient to allow complete refinement of the structure. Conformational analysis and electron diffraction represent complementary methods which will facilitate the determination of the structure. The necessary requirements for the x-ray approach are crystallinity and orientation. X-ray data cannot be Obtained from an amorphous sample which means that a noncrystalline polymeric material must be treated in order to induce or improve crystallinity. Some polymers, such as cellulose andchitin, are crystalline and oriented in the native state.(1 )... 

When a natural polysaccharide is amorphous, a film or a fiber must be cast, starting from a solution subsequent annealing and stretching provides a crystalline and oriented sample. The treament sequence usually involves stretching the sample at high humidity (or relatively high temperature for a thermoplastic), followed by annealing treatment with the sample kept under tension to maintain orientation. 

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