We investigated the effects of finite lengths of polymer chains on the structural and mechanical properties of polyethylene (PE) fibers with atomistic molecular dynamics simulations. PE fiber models containing long but finite chains with different distributions of chain-end defects were prepared from the orthorhombic crystalline PE configuration. In our main PE fiber model, chain-end defects were uniformly spaced along the chain direction with chain ends located at boundaries of multiple crystalline regions, which is consistent with the distribution of chain ends found in semicrystalline PE. At the early stage of tensile deformations before the yield point, a mismatch of conformational preferences in the chain-end region of a chain and chain segments away from the chain-end regions in neighboring chains developed gradually. Near the yield point, this mismatch in conformational preferences triggered a yield behavior associated with chain slippage near the chain-end region and caused significant changes in the structural and mechanical properties. After the yield point, the pattern of changes in effective lattice parameters estimated with the PE fiber model with finite chains was significantly different from that estimated with the crystalline PE without chain ends but was in an excellent agreement with those observed in recent experiments on PE fibers and preoriented high-density PE films. Rotations of chains in specific directions in response to the conformational mismatch with neighboring chains caused the observed pattern of changes in lattice parameters.

中文翻译：

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链的有限长度对聚乙烯纤维结构和力学性能的影响

我们通过原子分子动力学模拟研究了聚合物链的有限长度对聚乙烯（PE）纤维的结构和机械性能的影响。PE纤维模型包含长而有限的链，链端缺陷分布不同，这是由正交晶态PE构造制成的。在我们的主要PE纤维模型中，链端缺陷沿链条方向均匀分布，链端位于多个晶体区域的边界，这与半结晶PE中链端的分布一致。在屈服点之前的拉伸变形的早期阶段，构象偏好在链的链端区域和远离相邻链的链端区域的链段的构象失配逐渐发展。在屈服点附近 构象偏好的这种不匹配触发了与链端区域附近的链滑移相关的屈服行为，并导致了结构和机械性能的重大变化。在屈服点之后，用有限链的PE纤维模型估算的有效晶格参数的变化模式与不带链端的结晶PE估算的模式显着不同，但与最近在PE纤维上进行的实验中观察到的相吻合和预取向的高密度PE膜。响应于与相邻链的构象不匹配，链沿特定方向的旋转导致观察到的晶格参数变化模式。