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

IF 5.1 1区化学 Q1 POLYMER SCIENCE

Macromolecules Pub Date : 2025-04-29 DOI:10.1021/acs.macromol.5c00078

Haokun Xiao, Jianjian Huang, Xiaowen Bian, Mengmeng Wang, Xianrong Liang, Maoyuan Li, Gang Jin

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Abstract

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 crystalline regions of PET. Finally, the mechanism of strain-induced anisotropy of the refractive index and absorption coefficient was elucidated, which originates from the orientation of the molecular chain during necking and undergoes rapid changes once necking occurs. These insights deepen the understanding of the refractive index and absorption in the THz frequency range and provide an effective method for simultaneously characterizing the ordered structures in the amorphous and crystalline regions.

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晶体和非晶区同时取向测量中有序聚合物结构的太赫兹双折射和各向异性吸收特性

应变诱导结晶（SIC）是半结晶聚合物中最重要的现象之一。在拉伸过程中，晶态和非晶态区域出现有序结构，并伴随着复杂的演化过程。晶体区域的有序结构通常是一个完美的晶体，而非晶区域的有序结构主要由局部有序的链段组成。由于有序结构尺度的差异，同时表征晶态和非晶态有序结构面临着巨大的挑战。本研究提出了一种基于太赫兹时域光谱（THz-TDS）同时测量晶体和非晶态有序结构的方法，该方法对长程有序结构具有极高的灵敏度。建立了太赫兹波段的取向与双折射和吸收各向异性模型。研究了不同拉伸比下样品折射率和吸收系数的变化规律。结果表明，双折射与反式构象的取向成正比，并在太赫兹波段验证了取向-双折射模型。拉伸PET的吸收光谱中有1.3 ~ 2.3 THz和2.3 ~ 3.0 THz两个特征吸收带，与PET非晶区和结晶区反式构象的含量和取向密切相关。最后阐明了折射率和吸收系数的应变诱导各向异性的机理，这种各向异性源于缩颈过程中分子链的取向，并在缩颈发生后发生快速变化。这些见解加深了对太赫兹频率范围内的折射率和吸收的理解，并为同时表征非晶和晶体区域的有序结构提供了有效的方法。

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来源期刊

Macromolecules 工程技术-高分子科学

CiteScore

9.30

自引率

16.40%

发文量

942

审稿时长

2 months

期刊介绍： Macromolecules publishes original, fundamental, and impactful research on all aspects of polymer science. Topics of interest include synthesis (e.g., controlled polymerizations, polymerization catalysis, post polymerization modification, new monomer structures and polymer architectures, and polymerization mechanisms/kinetics analysis); phase behavior, thermodynamics, dynamic, and ordering/disordering phenomena (e.g., self-assembly, gelation, crystallization, solution/melt/solid-state characteristics); structure and properties (e.g., mechanical and rheological properties, surface/interfacial characteristics, electronic and transport properties); new state of the art characterization (e.g., spectroscopy, scattering, microscopy, rheology), simulation (e.g., Monte Carlo, molecular dynamics, multi-scale/coarse-grained modeling), and theoretical methods. Renewable/sustainable polymers, polymer networks, responsive polymers, electro-, magneto- and opto-active macromolecules, inorganic polymers, charge-transporting polymers (ion-containing, semiconducting, and conducting), nanostructured polymers, and polymer composites are also of interest. Typical papers published in Macromolecules showcase important and innovative concepts, experimental methods/observations, and theoretical/computational approaches that demonstrate a fundamental advance in the understanding of polymers.