We present a coarse-grained (CG) model of polyamide 6 (PA6) that captures the hydrogen bonding interactions between amide groups by embedding small charged beads within larger CG beads. This CG model balances the necessary atomic details and efficient coarse-graining, enabling crystallization simulations of PA6 on larger length and time scales. The results reveal a two-step structural adjustment during crystallization: hydrogen bonding layers form rapidly, followed by significant ordering and elongation of the stem length. Moreover, we explore the heterogeneous distribution of local stress across the semicrystalline structure for various polymer systems. A strong correlation between the local stress and order parameters is observed in systems without hydrogen bonding interactions, while the one in the PA6 system is notably weaker. By decomposing the local stress contributions from different bead types, we attribute this weak correlation to the superposition of varying correlations from the backbone and amide groups, which highlights the influence of hydrogen bonds on the local stress distributions. Our analysis of local stress tensors at the atomic level in semicrystalline polymers represents a critical step toward bridging the gap between microscopic structural properties and macroscopic mechanical behavior.

中文翻译：

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氢键聚合物中的结晶和异质局部应力分布：聚酰胺 6 （PA6） 的分子动力学模拟


我们提出了一种聚酰胺 6 （PA6） 的粗粒 （CG） 模型，该模型通过将带电的小珠子嵌入较大的 CG 珠子中来捕获酰胺基团之间的氢键相互作用。该 CG 模型平衡了必要的原子细节和高效的粗粒化，从而能够在更大的长度和时间尺度上对 PA6 进行结晶模拟。结果揭示了结晶过程中的两步结构调整：氢键层迅速形成，然后是茎长度的显着排序和伸长。此外，我们还探讨了各种聚合物系统在半结晶结构中局部应力的异质分布。在没有氢键相互作用的系统中观察到局部应力和有序参数之间的强相关性，而 PA6 系统中的相关性明显较弱。通过分解不同珠子类型的局部应力贡献，我们将这种弱相关性归因于主链和酰胺基团的不同相关性叠加，这突出了氢键对局部应力分布的影响。我们对半结晶聚合物中原子水平局部应力张量的分析代表了弥合微观结构特性和宏观机械行为之间差距的关键一步。