Injection molding of thermotropic liquid-crystalline polymers (TLCPs) can result in molded articles the exhibit complex orientation states that vary considerably as a function of depth in the part. Skin-core morphologies are often observed in TLCP moldings. Given that both core and skin orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two-dimensional wide-angle X-ray scattering (WAXS) in transmission and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4 -dihydroxy-?-methylstilbene (DH?MS)-based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is presented as a non-invasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm and does not require slicing or ultramicrotoming of the samples. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on- and off- axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission which are dominated by the microstructure in the skin and core regions. Qualitative comparisons are also made with 2D WAXS results from the literature.
Citation: Journal of Physics D-Applied Physics
Pub Type: Journals
injection molding, liquid crystalline polymer (LCP), NEXAFS, orientation