Atomistic Modeling of Plastic Deformation in Semicrystalline Polyethylene: Role of Interphase Topology, Entanglements, and Chain Dynamics,Macromolecules

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Atomistic Modeling of Plastic Deformation in Semicrystalline Polyethylene: Role of Interphase Topology, Entanglements, and Chain Dynamics
Macromolecules ( IF 5.1 ) Pub Date : 2020-06-08 , DOI: 10.1021/acs.macromol.9b02308
Raghavan Ranganathan _{1,

2} , Vaibhaw Kumar ₁ , Alexander L. Brayton ₁ , Martin Kröger ₃ , Gregory C. Rutledge ₁

Affiliation

The effects of interphase topology, entanglements, and chain dynamics on the mechanical response of semicrystalline polyethylene have been examined using atomistic simulations. In particular, the prevalence of the cavitation and melting/recrystallization mechanisms for yield and plastic flow were found to depend on both topological and dynamical properties of the molecular segments in the semicrystalline interphase. First, two different protocols were used during preparation of the interphase ensemble to modulate the distribution of (i) loops, bridges, and tails and (ii) entanglements within the noncrystalline domain. A protocol denoted “step-wise cooling” produced structures having a large fraction of long, entangled segments that yielded by the melting/recrystallization mechanism about 50% of the time. By contrast, the protocol denoted “instantaneous quench” produced structures that yielded by melting/recrystallization about 73% of the time. Second, two different united atom force fields, PYS and TraPPE-UA, that exhibit nearly identical topological characteristics of the noncrystalline domain but different mobilities were used to study the effect of chain dynamics on yield mechanisms. At the slower strain rate used in this work, yield and plastic flow proceeded exclusively via cavitation for the model using the TraPPE-UA force field, whereas both cavitation and melting/recrystallization were observed for the model using the PYS force field. The greater prevalence of melting/recrystallization in the latter case is attributed to faster chain-sliding dynamics in the crystalline domain. The dependences of the yield mechanism on topology and dynamics are found to be related.

中文翻译：

半结晶聚乙烯中塑性变形的原子建模：相间拓扑，缠结和链动力学的作用

已经使用原子模拟检查了相间拓扑，缠结和链动力学对半结晶聚乙烯的机械响应的影响。尤其是，发现空化和熔融/重结晶机制对屈服和塑性流动的普遍性取决于半晶间相中分子链段的拓扑和动力学性质。首先，在相间集合的准备过程中使用了两种不同的协议来调节（i）环，桥和尾以及（ii）非晶域内的纠缠的分布。表示为“逐步冷却”的方案产生的结构具有很大的纠缠长的链段，这些链段通过熔化/重结晶机理产生的时间约为50％。相比之下，该协议表示为“瞬时淬火”，所产生的结构大约在73％的时间内通过熔化/重结晶而产生。其次，两个不同的联合原子力场PYS和TraPPE-UA表现出几乎相同的非晶域拓扑特征，但使用不同的迁移率来研究链动力学对屈服机理的影响。在这项工作中使用的较慢应变速率下，使用TraPPE-UA力场对模型进行的空化仅通过空化进行，而对于使用PYS力场的模型，均观察到了空化和熔融/再结晶。在后一种情况下，熔化/重结晶的发生率较高是由于晶域中链滑动动力学更快。

更新日期：2020-06-23

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