Abstract

At terahertz frequencies, the torsional vibration motion is associated with dielectric relaxation in disordered solids with hydrogen bonds. The interaction between these processes is still poorly understood, especially at temperatures below the glass transition temperature especially important for the molecular mobility in polymers. We studied polymers with hydrogen bonds (polyamide-6 and polyvinyl chloride) at temperatures from 90 to 400 K using far IR spectroscopy in the range of 0.25–4 THz. The following three common features were observed in the spectrum of dielectric losses ε''(ν): (i) at temperatures well below the glass transition temperature (T_g), these losses are represented by the low-frequency wing of the absorption peak due to libration of monomer units of the polymers; (ii) in the range of 0.7T_g < T < T_g, additional temperature dependent losses are observed, which may be associated with the manifestation of secondary relaxation processes; (iii) at temperatures above T_g, the primary α relaxation processes predominantly contribute to terahertz losses. The obtained results show that the evolution of terahertz losses with temperature is caused by a change in the structure of hydrogen bonds, which seems to be common for systems with similar intermolecular interactions.

中文翻译：

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具有氢键的聚合物在太赫兹频率下弛豫过程与局部动力学相互作用的温度演化

摘要

在太赫兹频率下，扭转振动运动与具有氢键的无序固体中的介电弛豫有关。这些过程之间的相互作用仍然知之甚少，尤其是在低于玻璃化转变温度的温度下，这对于聚合物中的分子迁移率尤其重要。我们使用 0.25-4 THz 范围内的远红外光谱在 90 至 400 K 的温度下研究了具有氢键的聚合物（聚酰胺 6 和聚氯乙烯）。_{在介电损耗 ε''( ν} ) 谱中观察到以下三个共同特征： (i) 在远低于玻璃化转变温度 ( Tg ) 的温度下)，这些损失由聚合物单体单元的释放引起的吸收峰的低频翼表示；(ii) 在 0.7 T _g < T < T _g范围内，观察到额外的温度相关损失，这可能与二次弛豫过程的表现有关；(iii) 在高于T _g的温度下，主要的 α 弛豫过程主要导致太赫兹损耗。获得的结果表明，太赫兹损耗随温度的演变是由氢键结构的变化引起的，这对于具有相似分子间相互作用的系统来说似乎很常见。