为探讨聚合物分子的极性对其介电性质的影响, 采用太赫兹时域光谱研究了5种聚合物材料, 高密度聚乙烯、聚对苯二甲酸乙二醇酯、聚氨酯、聚偏氟乙烯和聚乙烯吡咯烷酮在太赫兹波段的吸收色散性质, 并尝试采用Debye模型对实验结果进行了理论分析.研究发现, 聚合物的偶极弛豫运动随极性的增强而加剧, 导致吸收系数(α)、介电常数虚部(ε")和弛豫强度(Δε)均随之增大; 由于弛豫运动受介质阻尼的影响落后于太赫兹电场的周期性变化, 折射率(n)和介电常数实部(ε')呈现反常的色散现象, 即n和ε'随频率的增大而降低; Debye模拟结果还表明弛豫时间(τ)随偶极子尺寸的增大和分子刚性的增强而显著增大.

To exploring the effect of polarity on dielectric properties of polymers, the absorption and dispersion characteristics of 5 polymers (high density polyethylene (HDPE), polyethylene terephthalate (PET), polyurethane (PU), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF)) in terahertz band were studied with terahertz time-domain spectroscopy (THz-TDS). Theoretical analysis was conducted by fitting the experimental results to Debye formula. It was demonstrated from the study that dipolar polarization occurred and was enhanced with the increase of the polymer polarity, which is responsible for the increment of absorption coefficient (α), imaginary part of dielectric constant (ε") and relaxation strength (Δε). It was known that the relaxation of dipole following behind the periodical variety of THz electric field was due to the medium damping effect. As a result, abnormal dispersion behavior happened. It was found that both the refractive index (n) and the real part of dielectric constant (ε')was decreased with the increase of frequency. The relaxation time (τ) obtained from Debye fitting was also found to increase significantly with the dipole size and the rigidity of molecular.