Fiber Diffraction Methods

Abstract

X-ray diffraction can be used to help determine the molecular geometry of polymers that prefer to be long helices rather than more complexly folded structures. It is usually possible to prepare specimens in which such helical molecules are aligned with their long axes parallel. Often further lateral organization occurs, but rarely to the degree of a three-dimensionally ordered single crystal. Potentially this is an advantage, since there is more information (about the Fourier transform (1, 2, 3) of a molecular structure) in the continuous intensity distribution in the diffraction pattern from a less well-ordered system than there is the "sampled" distribution characteristic of a single crystal. But, since "sampling" also implies local amplification of the molecular transform (at reciprocal lattice points), its absence results in much weaker diffraction signals and the theoretical advantage of knowing the continuous intensity variation is offset by the experimental difficulty of recording it accurately. A