Koh Miharu, Kitt Jay P, Pendergast Andrew D, Harris Joel M, Minteer Shelley D, Korzeniewski Carol
Department of Chemistry, University of Utah, Salt Lake City, Utah, USA.
Department of Chemistry, Missouri University of Science and Technology, Rolla, MO, USA.
Appl Spectrosc. 2025 Jan 17:37028241310904. doi: 10.1177/00037028241310904.
Crystallization from the melt is a critical process governing the properties of semi-crystalline polymeric materials. While structural analyses of melting and crystallization transitions in bulk polymers have been widely reported, in contrast, those in thin polymer films on solid supports have been underexplored. Herein, in situ Raman microscopy and self-modeling curve resolution (SMCR) analysis are applied to investigate the temperature-dependent structural changes in poly(ethylene oxide) (PEO) films during melting and crystallization phase transitions. By resolving complex overlapping sets of spectra, SMCR analysis reveals that the thermal transitions of 50 µm thick PEO films comprise two structural phases: an ordered crystalline phase and a disordered amorphous phase. The ordered structure of the crystalline PEO film entirely disappears as the polymer is heated; conversely, the disordered structure of the amorphous PEO film reverts to the ordered structure as the polymer is cooled. Broadening of the Raman bands was observed in PEO films above the melting temperature (67 °C), while sharpening of bands was observed below the crystallization temperature (45 °C). The temperatures at which these spectral changes occurred were in good agreement with differential scanning calorimetry (DSC) measurements, especially during the melting transition. The results illustrate that in situ Raman microscopy coupled with SMCR analysis is a powerful approach for unraveling complex structural changes in thin polymer films during melting and crystallization processes. Furthermore, we show that confocal Raman microscopy opens opportunities to apply the methodology to interrogate the structural features of PEO or other surface-supported polymer films as thin as 2 µm, a thickness regime beyond the reach of conventional thermal analysis techniques.
从熔体中结晶是决定半结晶聚合物材料性能的关键过程。虽然大量聚合物的熔融和结晶转变的结构分析已有广泛报道，但相比之下，固体载体上聚合物薄膜的此类分析却未得到充分探索。在此，原位拉曼显微镜和自建模曲线分辨（SMCR）分析被用于研究聚环氧乙烷（PEO）薄膜在熔融和结晶相变过程中随温度变化的结构变化。通过解析复杂的重叠光谱集，SMCR分析表明，50 µm厚的PEO薄膜的热转变包括两个结构相：有序的结晶相和无序的非晶相。随着聚合物被加热，结晶PEO薄膜的有序结构完全消失；相反，随着聚合物冷却，非晶PEO薄膜的无序结构恢复为有序结构。在高于熔点（67 °C）的PEO薄膜中观察到拉曼谱带变宽，而在低于结晶温度（45 °C）时观察到谱带变窄。这些光谱变化发生的温度与差示扫描量热法（DSC）测量结果高度一致，尤其是在熔融转变期间。结果表明，原位拉曼显微镜与SMCR分析相结合是揭示聚合物薄膜在熔融和结晶过程中复杂结构变化的有力方法。此外，我们表明，共聚焦拉曼显微镜为将该方法应用于研究厚度低至2 µm的PEO或其他表面支撑聚合物薄膜的结构特征提供了机会，这一厚度范围是传统热分析技术无法企及的。
