Hall Kyle Wm, Sirk Timothy W, Percec Simona, Klein Michael L, Shinoda Wataru
Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
Institute for Computational Molecular Science, Temple University, Philadelphia, PA 19122, USA.
Polymers (Basel). 2020 Feb 14;12(2):447. doi: 10.3390/polym12020447.
This study demonstrates that monodisperse entangled polymer melts crystallize via the formation of nanoscale nascent polymer crystals (i.e., nuclei) that exhibit substantial variability in terms of their constituent crystalline polymer chain segments (stems). More specifically, large-scale coarse-grain molecular simulations are used to quantify the evolution of stem length distributions and their properties during the formation of polymer nuclei in supercooled prototypical polyethylene melts. Stems can adopt a range of lengths within an individual nucleus (e.g., ∼1-10 nm) while two nuclei of comparable size can have markedly different stem distributions. As such, the attainment of chemically monodisperse polymer specimens is not sufficient to achieve physical uniformity and consistency. Furthermore, stem length distributions and their evolution indicate that polymer crystal nucleation (i.e., the initial emergence of a nascent crystal) is phenomenologically distinct from crystal growth. These results highlight that the tailoring of polymeric materials requires strategies for controlling polymer crystal nucleation and growth at the nanoscale.
本研究表明，单分散缠结聚合物熔体通过形成纳米级新生聚合物晶体（即晶核）而结晶，这些晶核在其组成的结晶聚合物链段（茎）方面表现出很大的变异性。更具体地说，大规模粗粒分子模拟用于量化过冷典型聚乙烯熔体中聚合物晶核形成过程中茎长度分布及其性质的演变。在单个晶核内，茎可以具有一系列长度（例如，约1 - 10纳米），而两个尺寸相当的晶核可以具有明显不同的茎分布。因此，获得化学单分散的聚合物样品不足以实现物理均匀性和一致性。此外，茎长度分布及其演变表明，聚合物晶体成核（即新生晶体的初始出现）在现象学上与晶体生长不同。这些结果突出表明，聚合物材料的定制需要在纳米尺度上控制聚合物晶体成核和生长的策略。
