Characterization of the skin orientation of thermotropic liquid-crystalline copolyester moldings with near-edge X-ray absorption fine structure

The process of injection-molding net-shape parts from thermotropic liquid-crystalline polymers results in a skin-core macrostructure. The underlying orientation in the core and the skin may differ both in magnitude and direction. A combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and two-dimensional wide-angle X-ray scattering (2D WAXS) in transmission was used to characterize the orientation in injection-molded plaques fabricated from thermotropic liquid-crystalline copolyesters based on either 4,4′-dihydroxy-a-methylstilbene or 6-hydroxy-2-naphthoic acid/6-hydroxybenzoic acid. NEXAFS is presented as a noninvasive in situ means of determining surface layer orientation that samples to a depth of as little as 2 nm and does not require slicing or ultramicrotoming of the samples. The effects of various processing conditions on the surface orientation in the region of the centerline of square injection-molded plaques are presented and discussed. Comparisons are made between orientation parameters obtained by 2D WAXS in transmission, which is dominated by the microstructure in the core, and the NEXAFS technique.