Terahertz (THz) spectroscopy was used to observe adsorbed water structure and dynamics within polymer films, ultimately providing a strong rationale for the observed rates of water desorption. The THz absorption spectra of nylon-6 films undergo drastic changes during the hydration and drying processes. Additionally, the structural change from γ to α crystals, induced by the hydration, was observed by the characteristic band of α-nylon-6 at 6.5 THz. Importantly, the THz spectra of adsorbed water, as well as deuterated water, within in the nylon films were observed by the continuous measurement of α-nylon during dehydration. The difference spectra clearly show three absorption bands of water molecules named Peaks I-III, which behave differently between the H2O and D2O materials. The spectra were assigned using a combination of ab initio molecular dynamics simulations and solid-state density functional theory calculations and were compared to previous spectral assignments of bulk water. The results show that the inclusion of H2O and D2O into polymer films results in a distinct set of spectral features that, while similar in frequencies to the dynamics of bulk water, represent significantly different motions owing to the unique chemical environment within the material. These results highlight the significant utility of using THz spectroscopy to study the hydration dynamics and spectral signatures of bound water in this important class of materials.

中文翻译：

---

用太赫兹光谱探索尼龙聚合物中束缚水的动力学。

太赫兹（THz）光谱用于观察聚合物膜中吸附的水结构和动力学，最终为观察到的水解吸速率提供了有力的依据。在水合和干燥过程中，尼龙6薄膜的太赫兹吸收光谱发生剧烈变化。另外，通过水合引起的从γ到α晶体的结构变化通过在6.5THz处的α-尼龙-6的特征带观察到。重要的是，通过在脱水过程中连续测量α-尼龙，可以观察到尼龙膜内部的吸附水以及氘化水的THz光谱。差异光谱清楚地显示了水分子的三个吸收带，称为峰I-III，它们在H2O和D2O材料之间的行为不同。使用从头算分子动力学模拟和固态密度泛函理论计算的组合分配光谱，并将其与大量散装水的先前光谱分配进行比较。结果表明，将H2O和D2O包含在聚合物薄膜中会产生一组独特的光谱特征，这些光谱特征的频率与散装水的动力学相似，但由于材料内部独特的化学环境，它们表现出明显不同的运动。这些结果突显了使用太赫兹光谱学研究这种重要材料类别中结合水的水合动力学和光谱特征的重要实用性。结果表明，将H2O和D2O包含在聚合物薄膜中会产生一组独特的光谱特征，这些光谱特征的频率与散装水的动力学相似，但由于材料内部独特的化学环境，它们表现出明显不同的运动。这些结果突显了使用太赫兹光谱学研究这种重要材料类别中结合水的水合动力学和光谱特征的重要实用性。结果表明，将H2O和D2O包含在聚合物薄膜中会产生一组独特的光谱特征，这些光谱特征的频率与散装水的动力学相似，但由于材料内部独特的化学环境，它们表现出明显不同的运动。这些结果突显了使用太赫兹光谱学研究这种重要材料类别中结合水的水合动力学和光谱特征的重要实用性。