Molecular Dynamics Simulations of the Effects of Entanglement on Polymer Crystal Nucleation,Macromolecules

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Molecular Dynamics Simulations of the Effects of Entanglement on Polymer Crystal Nucleation
Macromolecules ( IF 5.1 ) Pub Date : 2022-06-15 , DOI: 10.1021/acs.macromol.2c00817
Lingyi Zou ₁ , Wenlin Zhang ₁

Affiliation

We investigate the effects of entanglement on polymer crystallization using atomistic molecular dynamics simulations of linear and cyclic polyethylene (PE). While linear chains entangle with their neighbors, unlinked rings adopt compact conformations and do not exhibit conventional entanglements. By isotropically compressing linear chains, we also systematically reduce the entanglement density in PE melts without enhancing any local order that may promote crystallization. After demonstrating that the linear and cyclic chains exhibit similar crystal melting temperatures, we quantitatively show that the isothermal nucleation rate of PE increases with decreasing entanglement density at similar degrees of supercooling. The effect of entanglement density on crystal nucleation, however, is mild. The absence of conventional entanglements in unlinked rings only enhances the nucleation rate by a factor of two. Finally, using randomly linked and permanently entangled rings, which nucleate at a rate similar to that of the linear counterparts, we show that polymer nucleation is local and does not require large-scale relaxation of polymer chains.

中文翻译：

纠缠对聚合物晶体成核影响的分子动力学模拟

我们使用线性和环状聚乙烯 (PE) 的原子分子动力学模拟来研究缠结对聚合物结晶的影响。虽然线性链与它们的邻居纠缠在一起，但未连接的环采用紧凑的构象并且不表现出传统的纠缠。通过各向同性压缩线性链，我们还系统地降低了 PE 熔体中的缠结密度，而不会增强任何可能促进结晶的局部有序性。在证明线性和环状链表现出相似的晶体熔化温度后，我们定量地表明，在相似的过冷度下，PE 的等温成核速率随着缠结密度的降低而增加。然而，纠缠密度对晶体成核的影响是温和的。在未连接的环中没有传统的纠缠只会将成核率提高两倍。最后，使用随机连接和永久纠缠的环，其成核速率与线性对应物相似，我们表明聚合物成核是局部的，不需要聚合物链的大规模松弛。

更新日期：2022-06-15

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