Surface characterization of carbon fiber by infrared spectroscopy

Fourier transform infrared (FT-IR) internal reflection spectroscopy and X-ray photoelectron spectroscopy (XPS) have been applied to investigate the surface of polyacrylonitrile-based carbon fibers treated by chemical oxidation and electrochemical oxidation. It has been found that infrared spectroscopy has the comparable sensitivity to XPS and that the amount of the functionality introduced at the fiber surface depends on the oxidation time for the case of chemical oxidation and on the electrolyte used for the case of electrochemical oxidation.; Infrared spectra of surface oxidized carbon fibers have been taken with different angles of incidence, polarization states, and internal reflection elements (IRE) to find the optimal condition by internal reflection spectroscopy. It has been found that the maximum peak area of a surface functional group is obtained by using S polarized light at a 30{dollar}spcirc{dollar} angle of incidence for the multiple reflection technique. However, the highest signal-to-noise ratio is observed if unpolarized light is used. Spectral simulations have been performed to understand the observed spectra of the surface oxidized carbon fibers using exact optical theory. In the spectral simulations, Fresnel's three-layered system has been adopted to model the IRE/oxidized layer/bulk carbon fiber system.; Optical theory has also been applied to model the baseline of the internal reflection spectra of carbon fibers. Spectral simulation reveals that the baseline of the spectra should change due to the optical tunneling phenomenon. Additionally, the sloping baseline typically observed for graphite-like materials is due to the dispersion of the optical constants, and not to the dispersion of the infrared beam penetration depth.