State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science, Fudan University, Shanghai 200433, China.
Soft Matter. 2017 Nov 15;13(44):8250-8263. doi: 10.1039/c7sm01892d.
We employ a rod-coil multiblock molecular chain model to investigate chain folding behavior, which is a significant characteristic in semicrystalline polymers, by using the method of self-consistent field theory (SCFT). Polymer chains with different conformations in crystalline and amorphous regions are described by rigid rod chains and flexible Gaussian chains, respectively. At present, we concentrate on the thermodynamic behaviors of polymer semi-crystals after the formation of the initial lamellar crystals. A new mechanism for lamellar thickening is proposed to realize that the end of lamellar thickening depends on the crystallinity degree. In other words, it is impossible for lamellae to develop into extended-chain crystals by means of lamellar thickening if crystallinity is limited to a certain degree. We further discuss the competition between crystalline and amorphous regions and its influence on crystallization behaviors, such as the formation of double lamellae, chain tilt, the anomalies and adjacent re-entry. The synergistic influences of the driving force of crystallization, interfacial energy and crystallinity degree on chain folding behavior are also investigated when the density anomalies in amorphous regions are excluded. Our model demonstrates advantages in accurately describing the mesoscopic layered structures of semicrystalline polymers based upon a microscopic chain model and provides at least a semi-quantitative thermodynamic picture for chain folding.
我们采用棒-圈多嵌段分子链模型，通过自洽场理论（SCFT）方法研究链折叠行为，这是半晶聚合物的一个重要特征。结晶区和非晶区中具有不同构象的聚合物链分别用刚性棒链和柔性高斯链来描述。目前，我们专注于初始片晶形成后聚合物半晶的热力学行为。提出了一种新的片层增厚机制，以实现片层增厚的终点取决于结晶度。换句话说，如果结晶度限制在一定程度内，那么通过片层增厚使片层发展成伸展链晶体是不可能的。我们进一步讨论了结晶区和非晶区之间的竞争及其对结晶行为的影响，例如双片层的形成、链倾斜、异常和相邻重入。当排除非晶区中的密度异常时，我们还研究了结晶驱动力、界面能和结晶度对半晶聚合物链折叠行为的协同影响。我们的模型基于微观链模型，在准确描述半晶聚合物的介观层状结构方面具有优势，并为链折叠提供了至少半定量的热力学图像。
