针对太赫兹技术在材料特征识别和探测领域的潜在应用以及高分子材料在太赫兹波段的指纹特征, 利用太赫兹时域光谱技术开展了PA66高分子材料在太赫兹波段的吸收光谱以及折射率、 介电常数等光学参数的实验与理论分析研究。 得到了PA66的太赫兹波段的光谱特征及吸收特征峰。 并利用密度泛函理论开展了PA66在0.1~10 THz范围内的分子振动频率的计算工作, 对比了理论计算数据和实验测试数据, 并进行了太赫兹光谱特征吸收峰的归属指认。 结果表明, 计算的PA66分子振动频率与太赫兹实验光谱具有较高的一致性, 并且太赫兹吸收光谱中的特征峰是分子中各基团的振动与太赫兹波频率的共振响应。 通过分析基团的振动模式, 对太赫兹光谱吸收特征峰归属进行指认: PA66材料在0.2~2.3 THz频段内多个特征峰主要由主链上酰胺基中CO, —NH基团的摆动以及大骨架C链中的—CH2非对称性振动产生。 其中, 0.77 THz处的特征峰归因于分子内强烈的CO和N—H的面外摆动, 1.56 THz处特征峰包含CO的面外摆动和C链上CH2的扭动, 而1.85 THz处特征峰主要归因于来自单体己二酸中CH2和CO键的面外摇摆。 中心频率约为4.57 THz处的特征峰, 包含了CO的面间摆动和来自单体己二胺中CH2的强烈扭动。 7.6 THz频率的吸收峰主要由CO的摆动和—CH2, —NH的剪切振动产生。 研究结果表明, 高分子材料对太赫兹波的吸收与分子中各基团的振动模式密切相关, 并且在太赫兹波段的振动吸收峰一般由主链和支链中各种官能团的摇摆振动、 扭曲振动以及分子间的相互作用而产生, 进而推论出非对称性、 含N、 O等元素官能团的极性高分子材料, 电负性的差异致使分子振动偶极矩较大, 在太赫兹波段容易产生指纹特征峰。 为利用太赫兹技术进行材料的结构分析和识别检测提供理论基础和技术支撑。

Polymer materials have peculiar fingerprint spectrum in terahertz (THz) band, which has a potential application in the field of materials feature recognition and detection. In this study, the absorption spectra of PA66 in the THz region was studied by using terahertz time domain spectroscopy. The refractive index and dielectric constants were measured and analyzed. And the THz absorption spectra of PA66 were obtained between 0.2 and 2.3 THz. Then the vibration frequencies of PA66 were calculated using density functional theory (DFT) in the range of 0.1~10 THz. The results show that the calculated vibration frequencies of PA66 are in good agreement with experimental absorption spectra. By analyzing the vibration modes of the molecular, the absorption peaks within 0. 2~2. 3THz are generated from the oscillation of CO, —NH groups and the asymmetric motions of —CH2 in the backbone. And the vibration peak at 0.77 THz is generated from an out-of-plane wagging of CO, —NH groups, the 1.56 THz band is due to a combination of an out-of-plane wagging of CO, —NH groups and a rotor motion of the —CH2 group, while the vibration peak at 1.85 THz is due to an out-of-plane oscillation of CO, —CH2 groups, which come from adipic acid. The band centered near 4.57 THz that represents several modes associated with an in-plane wagging of the CO groups and a rotor motion of —CH2 groups from adipic acid, and the 7.6 THz band are associated with a wagging of CO and a scissor motion of —CH2, —NH groups. The results show that the absorption features in the THz regime of polymer materials is associated with the vibration motions of various groups in molecules, and the absorption peaks are generally due to the motions of wagging, rotor, oscillation and the intermolecular interactions. In addition, the asymmetric polar polymer material with N, O atoms is apt to generate dipole moments for the difference in electronegativity. Therefore, it is easy to show fingerprint characteristic peaks in the THz band, which can provide the theoretical basis and technical support for the structural analysis and identification of materials using THz technology.