The influence of entanglement on the growth and melting of polymer crystals is investigated by using molecular dynamics simulations across systems with different entanglement densities. Reducing entanglement density leads to a slight decrease of crystal thickness L but an increase of melting temperature T_m. To elucidate the entanglement-related inverse relation between T_m and L, we introduce the fold surface free energy σ_f predominantly governed by the conformational entropy loss of amorphous segments. Reducing the entanglement density results in a decrease of σ_f. Combining the contributions of σ_f and L, a linear relation between T_m and σ_f/L is obtained, which is consistent with the prediction of the Gibbs–Thompson equation. Crystallization commonly accompanies with disentanglement, while crystal melting precedes before entanglement reconstruction. Considering the thermodynamic contribution of entanglement, polymer crystallization and melting are not two mutually reversible phase transitions, not only kinetically but also thermodynamically.

中文翻译：

---

纠缠在聚合物晶体生长和熔融中的作用：分子动力学模拟


通过对具有不同纠缠密度的系统使用分子动力学模拟来研究纠缠对聚合物晶体生长和熔融的影响。降低纠缠密度导致晶体厚度 L 略有降低，但熔融温度 T_m 升高。为了阐明 T_m 和 L 之间与纠缠相关的反关系，我们引入了主要由无定形段的构象熵损失控制的折叠表面自由能 σ_f。降低纠缠密度会导致 σ_f 降低。结合 σ_f 和 L 的贡献，得到了 T_m 和 σ_f/L 之间的线性关系，这与 Gibbs-Thompson 方程的预测一致。结晶通常伴随着解缠，而晶体熔化先于纠缠重建。考虑到纠缠的热力学贡献，聚合物结晶和熔化不仅在动力学上而且在热力学上都不是两个相互可逆的相变。