Molecular assembly of mesophase and isotropic pitches at their fused states

Abstract

Molecular assembly of mesophase and isotropic pitches at their fused states was examined using a polarized light optical microscope with a hot stage, high temperature 13C-NMR, and high temperature horizontal X-ray diffractometer. C(002) profile of the mesophase pitch and its peak position became much broader and shifted to lower angle, respectively, by the rising temperature up to 400°C. Analyses of the profiles suggest that the thickness and the content of stacked fraction were 20–60 Å and 65–80% at room temperature, and 18–32 Å and 50–70% at their spinning temperature, respectively. Chemical shift of aligned carbons in a high temperature 13C-NMR slightly shifted to the higher magnetic field with rising temperature, indicating that the layer of assembled aromatic molecules became thinner, while no increase of unaligned aromatic carbon was observable. The content of optical anisotropy under an optical microscope consistently stayed constant in its fused state, indicating that a phase of unordered molecules was not introduced by the vigorous molecular motion. The isotropic pitch gave no distinct profile of C(002) in XRD, no chemical shift of unaligned aromatic carbon in 13C-NMR, and complete isotropy under the optical microscope in its fused state although some stackings were observed by XRD at room temperature.