Results of X-ray and electron diffraction studies

From the width of the reflections of the wide-angle X-ray scattering (WAXS) fiber pattern the apparent size and the degree of perfection of the crystalline domains can be determined. In PpPTA the size and disorder parameters are strongly anisotropic. Normal to the chain axis the dimensions of the domains are 4-6 nm. Analysis of the meridional reflections shows that these fibers apparently have a paracrystalline structure with a longitudinal crystallite size of at least 25 nm and a lattice distortion parameter gu of 2-3%. Annealing at temperatures up to 600°C increases the lateral size to about 10 nm and the longitudinal size to about 80 nm, while gn decreases to about 

An interesting correlation between the lattice distortion parameter and the modulus of PpPTA fibers was observed by Barton.Extrapolation of the data to gu = 0Vo leads to a modulus of about 218 GN m which is close to the value of the theoretical modulus of the PpPTA chain (see Section 6.4.1). Because the fiber compliance is linearly dependent on the second moment of the orientation distribution of the chains (see Section 6.4.1), Barton s observation indicates that the distortion parameter is probably related to the orientation distribution, i.e. an increasing disorientation of the chains will apparently result in a larger distortion parameter. This is supported by the relation observed by Hindeleh and Abdo between the modulus and a crystallinity index. By extrapolation they found a modulus of about 200GNm at 100% crystallinity. 

Krenzer and Ruland applied a Fourier analysis to the meridional reflections of PpPTA. They concluded that an interpretation of the line broadening by lattice defects in terms of a one-dimensional paracrystalline disorder along the c-axis is not justified, but that the disorder is the result of local defects such as chain ends incorporated in the crystalline lattice. 

In the WAXS patterns of aromatic polyamides, often at least ten layer lines can be seen, which points to a high degree of order along the fiber axis direction. The overall appearance of the patterns is remarkably similar to the theoretically predicted patterns from curvilinear crystals discussed by Vainshtein.  

It appears that the imaging of crystal lattice fringes is instructive in the visualization of the microstructure of the fiber. This was accomplished for the first time for an organic polymer with PpPTA 

---

The presence of defects clusters in disordered solid solutions was confirmed by direct experimental methods (neutron diffraction, F NMR, EXAFS, etc.) as well as indirectly, using results of X-ray and electron diffraction studies of ordered fluorite-like phases having close compositions [7]. 

---