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Formation of Asymmetric Leaf-Shaped Crystals in Ultrathin Films of Oriented Polyethylene Molecules Resulting from High-Temperature Relaxation and Recrystallization
Macromolecules ( IF 5.1 ) Pub Date : 2019-12-26 , DOI: 10.1021/acs.macromol.9b02021 Huihui Li 1 , Duanzijing Liu 1 , Xinyun Bu 1 , Zhenzhen Zhou 1 , Zhongjie Ren 1 , Xiaoli Sun 1 , Renate Reiter 2 , Shouke Yan 1, 3 , Günter Reiter 2
Macromolecules ( IF 5.1 ) Pub Date : 2019-12-26 , DOI: 10.1021/acs.macromol.9b02021 Huihui Li 1 , Duanzijing Liu 1 , Xinyun Bu 1 , Zhenzhen Zhou 1 , Zhongjie Ren 1 , Xiaoli Sun 1 , Renate Reiter 2 , Shouke Yan 1, 3 , Günter Reiter 2
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We melted, annealed, and recrystallized ultrathin films of oriented polyethylene (PE) molecules prepared by melt-drawing. A large number of randomly oriented asymmetric leaf-shaped crystalline structures consisting of preferentially oriented lamellae were formed simultaneously, as observed by optical and atomic force microscopies. The structural arrangement within these leaf-shaped crystalline structures was identified by grazing incidence X-ray diffraction. These structures consisted of two distinct sections, both differing strongly from circular spherulites obtained by crystalizing an isotropic melt. Besides, regions containing groups of stacks of slightly inclined but well-aligned flat-on lamellae and regions of less orderly arranged edge-on lamellae were found. When increasing the annealing temperature and/or annealing time, a change in morphology from the leaf-shaped crystalline structures to spherulites with two symmetric “eyes” was observed. Intriguingly, the annealing times required for such a change in crystalline morphology were about four orders of magnitude longer than the longest bulk relaxation time (reptation time). Because the appearance of spherulites indicates that films became equilibrated and reached a state of an isotropic melt before recrystallization, we may conclude that oriented PE chains in ultrathin films possessed a long-term memory of the preparation-induced chain stretching. Considering that the morphology and relaxation kinetics of PE films depended appreciably on the substrate properties and film thickness, we conclude that the formation of asymmetric leaf-shaped crystalline structures was also affected by the interaction of PE chains with the substrate and spatial confinement. The present results may shed new light on slow relaxation and reorganization processes encountered when long-chain polymers became oriented during sample processing.
中文翻译：
高温松弛和重结晶导致定向聚乙烯分子超薄膜中不对称叶状晶体的形成
我们对通过熔体拉伸制备的定向聚乙烯（PE）分子的超薄膜进行了熔化，退火和重结晶。通过光学和原子力显微镜观察，同时形成了大量由优先取向的薄片组成的无规取向的不对称叶状晶体结构。这些叶片状晶体结构内的结构排列是通过掠入射X射线衍射确定的。这些结构由两个截然不同的部分组成，两者都与通过使各向同性熔体结晶而获得的圆形球晶有很大不同。此外，还发现了一些区域，这些区域包含成组的略微倾斜但排列良好的平板状叠层和不规则排列的边缘叠层薄板区域。当增加退火温度和/或退火时间时，观察到形态从叶状晶体结构到具有两只对称“眼睛”的球晶的变化。有趣的是，这种晶体形态变化所需的退火时间比最长的体弛豫时间（缩回时间）长约四个数量级。由于球晶的出现表明薄膜在重结晶之前已经达到平衡并达到各向同性的熔融状态，因此我们可以得出结论，超薄薄膜中的定向PE链对制备诱导的链拉伸具有长期记忆。考虑到PE膜的形貌和弛豫动力学在很大程度上取决于基材的性能和膜厚，我们得出的结论是，不对称叶状晶体结构的形成也受到PE链与底物的相互作用和空间限制的影响。本结果可能为长链聚合物在样品处理过程中取向时遇到的缓慢弛豫和重组过程提供新的思路。
更新日期：2019-12-27
中文翻译：
高温松弛和重结晶导致定向聚乙烯分子超薄膜中不对称叶状晶体的形成
我们对通过熔体拉伸制备的定向聚乙烯（PE）分子的超薄膜进行了熔化，退火和重结晶。通过光学和原子力显微镜观察，同时形成了大量由优先取向的薄片组成的无规取向的不对称叶状晶体结构。这些叶片状晶体结构内的结构排列是通过掠入射X射线衍射确定的。这些结构由两个截然不同的部分组成，两者都与通过使各向同性熔体结晶而获得的圆形球晶有很大不同。此外，还发现了一些区域，这些区域包含成组的略微倾斜但排列良好的平板状叠层和不规则排列的边缘叠层薄板区域。当增加退火温度和/或退火时间时，观察到形态从叶状晶体结构到具有两只对称“眼睛”的球晶的变化。有趣的是，这种晶体形态变化所需的退火时间比最长的体弛豫时间（缩回时间）长约四个数量级。由于球晶的出现表明薄膜在重结晶之前已经达到平衡并达到各向同性的熔融状态，因此我们可以得出结论，超薄薄膜中的定向PE链对制备诱导的链拉伸具有长期记忆。考虑到PE膜的形貌和弛豫动力学在很大程度上取决于基材的性能和膜厚，我们得出的结论是，不对称叶状晶体结构的形成也受到PE链与底物的相互作用和空间限制的影响。本结果可能为长链聚合物在样品处理过程中取向时遇到的缓慢弛豫和重组过程提供新的思路。
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