No abstract

Many materials, especially polymers, have a substantial volume fraction without crystalline order. Though these regions are often termed amorphous, they frequently have specific local order. We describe and use here a method based on a non-energy-dispersive X-ray diffraction technique to obtain good quality interference functions and, by Fourier transform, radial distribution functions of the amorphous structures of polymers. We apply this approach to a family of electronic polymers of current interest, polyaniline, comparing polyaniline emeraldine base (EB-II prepared from NMP solution), polyaniline emeraldine salt (ES-II prepared by doping EB-II with HC1), and dedoped polyaniline ES-II salt. From these data, it is found that amorphous EB-II and ES-II show a local chain array resembling that exhibited by the recently determined EB-II and ES-II crystalline structures, respectively. Thus the order in "crystalline" and "amorphous" regions is locally similar but differs by the spatial range of structural correlations, a feature likely due to the amount of conformational defects. Dedoped polyaniline ES-II salt has an increased interchain disorder through a local structural order intermediate between those of amorphous EB-II and ES-II. These studies demonstrate the importance of sample history in evaluating the physical properties of polyaniline and provide a structural origin for memory effects previously reported.