The non‐reactive OPLS‐AA force‐field is used to compare direct shock and Hugoniostat simulations of a melt of cis‐1,4‐polybutadiene at different shock velocities and with chain lengths up to 500 monomers. Both methods yield equivalent Hugoniot data with negligible influence of the chain length. However, it is found that the dynamical compression effects induce a time‐dependent anisotropy in the stress tensor in the direct shock simulations, yielding a non‐zero shear component. This anisotropy vanishes to the usual isotropic stress through two specific relaxation mechanisms: a fast process (characteristic time ≈1 ps) associated with the relaxation of the local intramolecular degrees of freedom of the chains, and a second slower process (characteristic time ≈100 ps) associated with the structural reorganisation of the polymer chains, involving long‐range intramolecular and intermolecular interactions. A third potential relaxation process, associated with entanglements, may be at play but is beyond the scope of the present study.

中文翻译：

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顺式1,4-聚丁二烯熔体中的恒电子稳定剂和直接电击模拟

非反应性OPLS-AA力场用于比较在不同冲击速度和链长不超过500个单体的情况下，顺式1,4-聚丁二烯熔体的直接冲击和Hugoniostat模拟。两种方法均产生等效的Hugoniot数据，而对链长的影响可忽略不计。但是，发现在直接冲击模拟中，动态压缩效应在应力张量中引起了随时间变化的各向异性，从而产生了非零的剪切分量。这种各向异性通过两种特定的弛豫机制逐渐消失为通常的各向同性应力：与局部分子内链自由度的弛豫相关的快速过程（特征时间≈1ps），以及第二个较慢的过程（特征时间≈100ps） ）与聚合物链的结构重组有关，涉及长期的分子内和分子间相互作用。与纠缠有关的第三个潜在的弛豫过程可能正在起作用，但超出了本研究的范围。