X-ray Diffraction from Polymers

New Jersey Center for Biomaterials, Rutgers University, Piscataway, NJ, USA 

Polymer Morphology Principles, Characterization, and Processing, First Edition. Edited by Qipeng Guo. 2016 John Wiley Sons, Inc. Published 2016 by John Wiley Sons, Inc. 

Therefore, rather than describing these methods, this chapter focuses on the aspects unique to polymeric materials. 

The diffracted intensities are recorded as a function of the scattering vector (or momentum transfer) q, which is related to the scattering angle 26 by the relation q= 4n sin 6)/A. When coherently scattered X-rays from atoms in neighboring planes interfere with each other, then Bragg s law (Eq. 2.1) holds  

TABLE 2.1 The Structural Parameters That Can he Derived from WAXS Data from Polymers in the Solid State 

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X-Ray Diffraction from Polymers with Mesomorphic Order... 

Unlike simple inorganic compounds (e.g., NaCl or KC1), polymers do not have a perfectly ordered crystal lattice formation and are not completely crystalline. In fact, they contain both crystalline and amorphous regions. Hence, the X-ray diffractions from them are found to be a mixture of sharp as well as diffused patterns. 

For polymers, a problem in identifying the reflections causes a problem in determining atomic arrangements from X-ray diffraction results. Polymers do not usually exhibit reflections greater than 4 or 5. Using oriented materials greatly simplifies data. 

Nye then turns to Polanyi s brilliant work on the X-ray diffraction of polymers and solids in general. In this field he was more successful, although some of his ideas were also developed independently by other scientists. Polanyi s main problem in this area was lack of support from his colleagues in Berlin. This was partly because his ideas were too advanced for the 1920s, but also reflects Polanyi s inability (or at least unwillingness) to follow the current trends. 

X-ray diffraction from liquid crystal polymers has been extensively used to determine the translational order of the mesogenic groups. For instance, in a smectic phase the layer spacing is easily determined from the... 

Poly(vinyl fluoride) [24981-14-4] (PVF) is a semicrystaltiae polymer with a planar, zig-zag configuration (50). The degree of crystallinity can vary significantly from 20—60% (51) and is thought to be primarily a function of defect stmctures. Wide-line nmr and x-ray diffraction studies show the unit cell to contain two monomer units and have the dimensions of a = 0.857 nm, b = 0.495 nm, and c = 0.252 nm (52). Similarity to the phase I crystal form of poly (vinytidene fluoride) suggests an orthorhombic crystal (53). 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

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