Lin Yuanfei, Chen Wei, Meng Lingpu, Wang Daoliang, Li Liangbin
National Synchrotron Radiation Laboratory, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei, China.
Soft Matter. 2020 Apr 15;16(15):3599-3612. doi: 10.1039/c9sm02554e.
The stretch-induced structural evolution mechanism is a long-standing scientific question in the post-stretching processing of polymer films. X-ray scattering, especially a combination of small- and wide-angle X-ray scattering (SAXS/WAXS), provides a powerful method to study the hierarchical structure of polymer films. Recent advances in synchrotron radiation (SR) light sources and detection techniques allow one to measure the structural evolution of polymer films during post-stretching processing in real time with ultrahigh time resolution, which benefits the understanding on this topic. This review summarizes some recent investigations on post-stretching processing of polymer films, which combine in situ X-ray scattering techniques with purposely designed tensile apparatus in terms of three aspects: uniaxial stretching, biaxial stretching and stretching with chemical reactions. Concerning the polymer bulk, traditional deformation mechanisms like stretch-induced crystallization (SIC), crystal slipping, phase transition and melting-recrystallization are discussed for the uniaxial and biaxial post-stretching of polymer films. New deformation models have been developed to focus on the structural evolution on the length scale of lamellar stacks, which consider the potential microphase separation of the interlamellar amorphous phase and microbuckling. For solution systems, the coupled effects of the mechanical work from external force and the chemical potential from possible chemical reactions are taken into account for the structural evolution during stretching in solution. Roadmaps of structural and morphological evolution in the processing parameter space (i.e., temperature, stress, strain and the concentration of additive in the bath solution) are eventually constructed for precursor films. The accumulation of a structural evolution database for post-stretching processing of polymer films can be expected to provide a helpful guide for industrial processing for high-performance polymers in the near future.
拉伸诱导的结构演变机制是聚合物薄膜后拉伸加工过程中一个长期存在的科学问题。X射线散射，尤其是小角和广角X射线散射（SAXS/WAXS）的结合，为研究聚合物薄膜的层级结构提供了一种强大的方法。同步辐射（SR）光源和检测技术的最新进展使人们能够以超高的时间分辨率实时测量聚合物薄膜在后拉伸加工过程中的结构演变，这有助于对该主题的理解。本综述总结了聚合物薄膜后拉伸加工的一些最新研究，这些研究将原位X射线散射技术与专门设计的拉伸装置结合起来，从单轴拉伸、双轴拉伸和化学反应拉伸三个方面进行了探讨。关于聚合物本体，讨论了聚合物薄膜单轴和双轴后拉伸中传统的变形机制，如拉伸诱导结晶（SIC）、晶体滑移、相变和熔融再结晶。已经开发了新的变形模型来关注片层堆叠长度尺度上的结构演变，该模型考虑了层间非晶相的潜在微相分离和微屈曲。对于溶液体系，考虑了外力作用下的机械功和可能化学反应产生的化学势对溶液拉伸过程中结构演变的耦合作用。最终构建了前驱体薄膜在加工参数空间（即温度、应力、应变和浴液中添加剂浓度）中的结构和形态演变路线图。预计聚合物薄膜后拉伸加工结构演变数据库的积累将在不久的将来为高性能聚合物的工业加工提供有益的指导。
