Abstract High-pressure synchrotron x-ray diffraction and vibrational spectroscopy (infrared absorption and Raman) in a diamond-anvil cell have been performed for polyethylene samples at pressures up to ∼10 GPa. These two techniques yield complementary information on the inter- and intra-molecular bonds and how they change as a function of volume. Three different samples of polyethylene were examined, including a high-density polyethylene, an ultra-high molecular weight polyethylene, and a crosslinked polyethylene. The diffraction peaks for the common orthorhombic Pnam phase continuously decreases in intensity as the pressure is increased and become unobservable at high pressure, while those for a monoclinic A2/m impurity phase initially present in all three samples remain relatively constant in intensity. The monoclinic A2/m phase has two chains per unit cell, as does the ambient pressure orthorhombic Pnam phase, which is consistent with the lack of a change in the vibrational mode splitting patterns as pressure is increased and the monoclinic phase becomes dominant. In addition, the pressure-induced correlation splitting of the infrared active C-H stretching vibrational modes has been observed for the first time.

中文翻译：

---

聚乙烯的高压 X 射线衍射和振动光谱：结构相变的证据

摘要 高压同步加速器 X 射线衍射和振动光谱（红外吸收和拉曼）已在金刚石砧室中对聚乙烯样品在高达 10 GPa 的压力下进行。这两种技术产生关于分子间和分子内键以及它们如何随体积变化的互补信息。检查了三种不同的聚乙烯样品，包括高密度聚乙烯、超高分子量聚乙烯和交联聚乙烯。随着压力的增加，普通正交 Pnam 相的衍射峰强度不断降低，在高压下变得不可观察，而最初存在于所有三个样品中的单斜 A2/m 杂质相的衍射峰强度保持相对恒定。单斜 A2/m 相每个晶胞有两条链，环境压力正交 Pnam 相也是如此，这与随着压力增加和单斜相成为主导而振动模式分裂模式没有变化是一致的。此外，首次观察到红外主动 CH 伸缩振动模式的压力诱导相关分裂。