Chemical state analysis of heat-treated polyacrylonitrile fiber using soft X-ray spectromicroscopy

Chemical state analyses of heat-treated polyacrylonitrile (PAN) fibers with a spatial resolution of 200 nm have been performed using scanning transmission X-ray microscopy (STXM) at a third generation synchrotron radiation facility. Near-edge X-ray absorption fine structure (NEXAFS) spectra and chemical state images have been obtained on the cross-sectioned fiber specimens. A clear `core–rim' structure has been observed in the heat-treated fibers. The spectral characteristics show that the fiber has less nitrile group in the core region, suggesting that, contrary to the model widely believed, the conversion of the nitrile to other chemical species proceeds faster in the core of the fibers.