[论文解读] Modeling of polymer phase transition from crystalline to conformationally disordered phase

V. V. Atrazhev, D. V. Dmitriev+1 more|arXiv (Cornell University)|Feb 27, 2026

Polymer crystallization and properties被引用 0

一句话总结

一个基于物理的分析模型描述聚合物从晶体相到构象无序相的相变，针对大气压下的分子动力学模拟进行标定，并在高压下验证。

ABSTRACT

A physics-based analytical model describing the phase transition from crystalline to conformationally disordered (condis) crystalline phase is developed. In the model, the free energy is written as a function of temperature and the lattice parameter (mean distance between neighboring chains). It consists of two contributions: elastic and conformational. The elastic contribution describes the interaction between neighboring chains, while the conformational part takes into account the conformation of one chain inside the potential tube, formed by the neighboring chains. To verify this approach, polyethylene - the simplest polymer possessing the condis phase - was chosen as a modeling object. Previous experiments and molecular dynamics simulations show that the typical conformation of a polymer chain in a crystalline phase consists mainly of trans dihedrals and a small fraction of gauche dihedrals, which can be considered as defects of the crystalline lattice. These defects displace the chain inside the tube thus increasing the potential energy. The energy required to form such a defect decreases rapidly with increasing distance between neighboring chains. This leads to a first-order phase transition at a certain temperature to the condis phase, in which distance between neighboring chains is large and a fraction of gauche dihedrals is high. This physical picture of the phase transition is described by the proposed analytical model, the parameters of which were calibrated against the results of molecular dynamics simulations for atmospheric pressure. The model predictions for the pressure of 500 atm and 1000 atm are in perfect agreement with the results of molecular dynamics simulations.

研究动机与目标

• 为聚合物的晶体到构象无序相转变建立一个基于物理的分析模型。
• 将自由能表示为温度与晶格参数（平均链间距）的函数。
• 捕捉邻近链之间的弹性相互作用以及由邻近链构成的潜在管中单链的构象能量。

提出的方法

• 将自由能分解为弹性贡献和构象贡献。
• 用弹性项描述链间相互作用。
• 在由邻近链定义的管中建模单链的构象能量。
• 在大气压下对模型参数进行分子动力学模拟的标定。
• 利用该模型预测相行为，并与在500 atm和1000 atm下的MD结果进行比较。

实验结果

研究问题

• RQ1 决定晶体到 condis 相过渡的自由能景观形式是什么？
• RQ2 当温度和链间距离变化时，弹性贡献和构象贡献如何驱动相变？
• RQ3 该解析模型能否再现MD观测到的转变压力和构象缺陷能量？

主要发现

• 该模型在链间距离增加、gauche 缺陷分数上升时产生第一类相变进入 condis 相。
• 随着邻近链距离增加，缺陷形成能快速下降，促进相变。
• 模型参数在大气压下与MD模拟进行标定。
• 对500 atm和1000 atm的预测与MD结果一致。
• condis 相的特征是链间距离更大、gauche 缺陷分数更高。