层状结构
微晶
结晶
板层(表面解剖学)
材料科学
分子动力学
聚乙烯
聚合物结晶
化学物理
高分子化学
摩尔质量分布
聚合物
化学工程
结晶学
化学
结晶度
计算化学
复合材料
有机化学
工程类
作者
Li Zhao,Yanling Hu,Yunqi Shao,Zhen Liu,Бо Лю,Xuelian He
摘要
By means of molecular dynamics simulations, extensional flow was performed on five polyethylene models with different molecular weight distributions (MWDs) precisely designed in view of Grubbs, metallocene, Ziegler-Natta, and chromium-based catalysts, while ignoring the sequence distributions of short branches to shed light on the molecular mechanism of MWD on shish-kebab formation. The formation of shish-kebab crystallites can be divided into three stages: the emergence of precursors, evolution from precursors to shish nuclei, and the formation of lamellar crystallites. The results demonstrated that the precursors initiated from trans-rich segments with local order and minor crystallinity grew into large shish nuclei and eventually evolved into lamellae. There were more inconsecutively trans-state bonds occurring in long chains rather than in short chains, which promoted an easier transformation from precursors to shish nuclei. Therefore, broader MWDs make positive contributions to the formation of shish nuclei, increase the crystallization speed, and the generation of a more regular, compact, and thicker lamella with less tie molecule fractions, while the final crystallinity is independent of MWD.
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