Terahertz Birefringence and Anisotropic Absorption Characteristic of Ordered Polymer Structures for Simultaneous Orientation Measurement in Crystalline and Amorphous Regions

作者：Haokun Xiao, Jianjian Huang, Xiaowen Bian, Mengmeng Wang, Xianrong Liang, Maoyuan Li, Gang Jin · 发表于：Macromolecules · 年份：2025 · DOI：10.1021/acs.macromol.5c00078 · 被引用次数：7 · 研究领域：Terahertz technology and applications、Acoustic Wave Resonator Technologies、Advanced Chemical Sensor Technologies

Strain-induced crystallization (SIC) is one of the most significant phenomena in semicrystalline polymers. During the stretching process, ordered structures occur in the crystalline and amorphous regions, accompanied by a complex evolution process. The ordered structure of the crystalline region is usually a perfect crystal, while that of the amorphous region mainly consists of locally ordered chain segments. The simultaneous characterization of ordered structures in both crystalline and amorphous regions faces significant challenges due to differences in the scale of the ordered structure. This research proposed a method for simultaneously measuring ordered structures of poly(ethylene terephthalate) (PET) in both crystalline and amorphous regions based on terahertz time-domain spectroscopy (THz-TDS) with extreme sensitivity to the long-range ordered structure. The models between orientation and birefringence and absorption anisotropy in the THz band were established. The evolution of the refractive index and absorption coefficient of samples at different draw ratios was investigated. The results showed that birefringence was proportional to the orientation of trans conformations, and the orientation–birefringence model was validated in the THz band. Then, two characteristic absorption bands, ranging within 1.3–2.3 and 2.3–3.0 THz, in the absorption spectra of stretched PET are closely related to the content and orientation of trans conformation in the amorphous and crystalli...