抄録
It is well known that a heat-treated poly-p-phenylenebenzobisoxazole(PBO)fiber gives an anisotropic four-point scattering pattern in small-angle X-ray scattering(SAXS)indicating growth of density fluctuations during the heat treatment. Many researchers inferred that the density fluctuations originate from density difference between crystal and amorphous regions in the PBO fiber. However, it is not fully clarified and the hypothesis is never experimentally proved yet. In order to elucidate the structural entity of the density fluctuations, the superstructure was investigated by direct observation of transmission electron microscopy(TEM)using defocus contrast(DFC)method. The obtained DFC image from a PBO fiber gave an intriguing contrast in the TEM micrograph and the 2-dimensional Fourier transform of the image gave a four-point pattern which strongly suggests that the contrast can be derived from the density difference corresponding to the density fluctuations giving rise to the SAXS pattern. Moreover, it is proved that higher density regions in the density fluctuations correspond to PBO crystals in the fiber because crystalline lattice fringes of the PBO fiber in the high-resolution image were inevitably located at the darker regions in the DFC image. This must be a first experimental evidence for the hypothesis based on the crystallization enhancement of density fluctuations in PBO fiber.
