Study on Thermodynamics of Polymer Crystallization Based on Twin-Lattice Model
Study on Thermodynamics of Polymer Crystallization Based on Twin-Lattice Model
复制标题
基于双晶格模型的聚合物结晶热力学研究
DOI：
10.1021/acs.jpcb.8b05991
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Yuliang Yang
中科院分区：
文献类型：
--
作者：
Nuofei Jiang;Ping Tang;Hongdong Zhang;Yuliang Yang
聚合物结晶是决定聚合物材料性能的最重要环节。本文将由Lennard-Jones和Devonshire提出的双晶格模型推广到描述聚合物结晶热力学。该模型考虑了链段的位置顺序和键的取向顺序。通过进一步引入构象能和熵，得到聚合物的自由能，并由此定义了一个新的参数，即构象能与位置扩散能之比。研究了聚合物结晶过程中的两类过程，即有塑性结晶相和无中间相的结晶过程。结晶过程的选择取决于晶格能和构象能的大小。从晶体到塑性晶体的固-固转变显示出对构象能的显著依赖性。考虑到数据的可靠性，选择正构烷烃作为聚合物的代表，比较模型的预测与实验观察。我们预测了旋转相消失的碳原子数，这与实验结果相当一致。这些计算和结果表明，该模型可以提供一个新的理解聚合物的结晶。
Polymer crystallization is the most important part in determining the performance of polymeric materials. The twin-lattice model originally provided by Lennard-Jones and Devonshire, developed by Pople and Karasz and other researchers, is extended for describing the thermodynamics of polymer crystallization. The positional order of segments and the orientational order of bonds are considered in this model. The free energy of polymers is obtained by further introducing the conformational energy and entropy, and thus a new parameter is defined, which is the ratio of conformational energy and positional diffusion energy. We studied two kinds of processes in polymer crystallization, including the process with plastic crystal phase and without any mesophases. The choice of crystallizing process is determined by the magnitude of lattice energy and conformational energy. The solid–solid transition from crystal to plastic crystal shows a significant dependence on the conformational energy. Considering data reliability,n-paraffins are chosen as the representation of polymers to compare the predictions of the model with experimental observations. We predict the number of carbons beyond which the rotator phase disappears, which is quite in agreement with the experiments. These calculations and results show this model can provide a new understanding to the crystallization of polymers.