Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides
Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides
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硬质聚酰亚胺薄膜中的链取向以及光学和介电性能的各向异性
DOI：
10.1002/polb.1992.090301203
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
J. Rabolt
中科院分区：
文献类型：
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作者：
D. Boese;Hyun;D. Yoon;J. Swalen;J. Rabolt
通过光波导、紫外-可见光 (UV-VIS)、红外 (IR) 和介电光谱对前体聚酰胺酸进行热酰亚胺化制备的聚对亚苯基联苯四甲酰亚胺 (BPDA-PDA) 薄膜进行了研究。聚酰亚胺薄膜在1064 nm波长处表现出非常大的折射率各向异性，其中面内折射率n∥ = 1.806和面外折射率n⊥ = 1.589。在大约 100μm 的薄膜之间没有发现薄膜厚度对该光学各向异性的明显影响。 2.1 和约。 7.8微米厚度。这种大的双折射归因于联苯四甲酰亚胺部分的平面平行于薄膜表面的优先取向，以及 BPDA-PDA 链沿薄膜平面排列的强烈偏好。面内折射率n∥的频率色散与根据洛伦兹-洛伦兹方程从紫外-可见光谱中计算出的结果一致，在170-500 nm区域表现出多个吸收带。 7000–400 cm,−1 范围内的红外吸收的贡献是通过测量光谱的斯皮策-克莱曼色散关系计算得出的，增加了约。 0.046至面内折射率n∥。倾斜角度相关的偏振红外结果表明面外折射率 n⊥ 几乎有相同的增加。与 ca 的测量值相比，应用麦克斯韦关系可得出 1.2 × 1013 Hz 时的面外介电常数 e⊥ ≃ 2.7。 106 赫兹时为 3.0。假设面内介电常数 e∥ 的这一微小差异保持不变，我们得到这些聚酰亚胺薄膜的介电性能非常大的各向异性，在 1.2 × 1013 Hz 时估计面内介电常数 e∥ ≃ 3.4，在 106 Hz 时 e∥ ≃ 3.7。 © 1992 约翰威利父子公司。
Thin films of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet-visible (UV-VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n∥ = 1.806 and the out-of-plane index n⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA-PDA chains to align along the film plane. The frequency dispersion of the in-plane refractive index n∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV-visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,−1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in-plane refractive index n∥. Tilt-angle–dependent polarized IR results indicate nearly the same increase for the out-of-plane index n⊥. Application of the Maxwell relation then leads to the out-of-plane dielectric constant e⊥ ≃ 2.7 at 1.2 × 1013 Hz, as compared with the measured value of ca. 3.0 at 106 Hz. Assuming this small difference to remain the same for the in-plane dielectric constants e∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant e∥ ≃ 3.4 at 1.2 × 1013 Hz, and e∥ ≃ 3.7 at 106 Hz. © 1992 John Wiley & Sons, Inc.