Interrogation of "surface," "skin," and "core" orientation in thermotropic liquid-crystalline copolyester moldings by near-edge x-ray absorption fine structure and wide-angle x-ray scattering
Interrogation of "surface," "skin," and "core" orientation in thermotropic liquid-crystalline copolyester moldings by near-edge x-ray absorption fine structure and wide-angle x-ray scattering
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DOI：
10.1002/app.26759
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发表时间：
2007-11-15
影响因子：
3
通讯作者：
Fischer, Daniel A.
中科院分区：
文献类型：
--
作者：
Rendon, Stanley;Bubeck, Robert A.;Fischer, Daniel A.
注射成型热致液晶聚合物（TLCP）通常会导致制造出具有复杂取向状态的成型制品，这些取向状态随厚度变化很大。在 TLCP 模制品中经常观察到“皮芯”形态。鉴于“芯”和“皮”取向状态通常在大小和方向上可能不同，这些复杂取向状态的反卷积需要一种方法来单独表征表面区域中的分子取向。结合使用透射中的二维广角 X 射线散射 (WAXS) 和近边缘 X 射线吸收精细结构 (NEXAFS) 光谱来探测由 4,4'-二羟基-α-甲基二苯乙烯 (DH α MS) 基热致液晶共聚酯制成的注塑板中的分子取向。部分电子产额 (PEY) 模式 NEX-AFS 是一种非侵入式非原位表征工具，具有精致的表面灵敏度，采样深度可达 2 run。介绍并讨论了板材几何形状和注塑加工条件对注塑板材中心线同轴和离轴区域表面取向的影响。对 NEXAFS 获得的取向参数与透射中的 2D WAXS 获得的取向参数进行了定量比较，这些取向参数主要由表皮和核心区域的微观结构决定。还与文献中的 2D WAXS 结果进行了一些定性比较。 (c) 2007 年 Wiley 期刊。
Injection molding thermotropic liquid-crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. "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 absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4 '-dihydroxy-alpha-methylstilbene (DH alpha MS)-based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEX-AFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 run. 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. Some qualitative comparisons are also made with 2D WAXS results from the literature. (c) 2007 Wiley Periodicals.