Thermal-Induced Structural Evolution of Melt-Stretched PA11: Direct Evidence for the Preservation of Hydrogen-Bonded Sheets Above the Brill Transition Temperature

IF 5.1 1区 化学 Q1 POLYMER SCIENCE
Ruixue Ma, Lijun Zhang, Zhen Zhang, Chongxin Huang, Haodong Huang, Wei Cao, Yanping Liu, Chuntai Liu, Zhen Wang
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Abstract

Despite extensive research into the thermally induced structural transitions of polyamides (PAs), the stability of hydrogen-bonded (H-bonded) sheets above the Brill transition temperature (TB) remains a contentious issue. Herein, we investigated the structural development of melt-stretched PA11 during heating and cooling cycles, utilizing in situ synchrotron wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy. By leveraging the unique twisted and oriented lamellar morphology created during melt stretching, we successfully identified and monitored, for the first time by WAXD, the H-bonded sheets across a broad temperature range up to the melting point (Tm). Our findings demonstrate that the H-bonded sheets are well maintained above TB until the sample fully melts, exhibiting distinct evolutionary trends in interplanar spacing, diffraction azimuth and orientation in response to temperature and melt-stretch ratio, compared to other crystallographic planes. The preserved H-bonded sheets have stronger interchain interactions, which impart a high anisotropy of thermal expansion to the high-temperature δ-phase. Further analysis of the FTIR data indicates that lattice variations below TB are driven by significant conformational twisting around the amide groups in the α′-phase, while thermal expansion predominantly dictates the variations in the δ-phase above TB. Additionally, the absence of notable alterations in H-bond interactions supports the continued stability of H-bonded sheets below Tm. This study enhances our understanding of the molecular mechanisms underlying thermally induced crystalline structural evolution in polyamide systems.

Abstract Image

熔融拉伸PA11的热诱导结构演化:在布瑞尔转变温度以上保存氢键片的直接证据
尽管对聚酰胺(PAs)的热诱导结构转变进行了广泛的研究,但在布里尔转变温度(TB)以上的氢键(h键)片的稳定性仍然是一个有争议的问题。在此,我们利用原位同步广角x射线衍射(WAXD)和傅里叶变换红外(FTIR)光谱研究了熔融拉伸PA11在加热和冷却循环中的结构变化。通过利用熔体拉伸过程中产生的独特的扭曲和定向片层形态,我们首次通过WAXD成功地在熔点(Tm)的宽温度范围内识别和监测了h键片。我们的研究结果表明,在样品完全熔化之前,h键片在TB以上保持良好,与其他晶体面相比,在面间距,衍射方位和取向方面表现出明显的变化趋势,这是对温度和熔体拉伸比的响应。保留的h键片具有较强的链间相互作用,使高温δ相的热膨胀具有较高的各向异性。进一步的红外光谱分析表明,TB以下的晶格变化是由α′相酰胺基团周围的构象扭曲驱动的,而TB以上的δ相变化主要是由热膨胀引起的。此外,氢键相互作用没有明显的变化,支持了h键片在Tm以下的持续稳定性。本研究增强了我们对聚酰胺体系中热诱导晶体结构演化的分子机制的理解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Macromolecules
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.
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