Analysis of spatial orientation distribution of highly oriented polyimide film using micro ATR-FTIR spectroscopic imaging method
Analysis of spatial orientation distribution of highly oriented polyimide film using micro ATR-FTIR spectroscopic imaging method
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DOI：
10.1016/j.polymer.2021.123616
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发表时间：
2021-03
期刊：
影响因子：
4.6
通讯作者：
R. Ishige;C. Song;S. Hara;S. Ando;S. Kazarian
中科院分区：
文献类型：
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作者：
R. Ishige;C. Song;S. Hara;S. Ando;S. Kazarian
采用偏振显微镜衰减全反射傅里叶变换红外吸收光谱（micro pATR-FTIR）成像技术，分析了芳香聚酰亚胺（PIs）及其前驱体聚酰胺酯（PAE）在双轴取向薄膜中的分子取向。将PAE的溶致液晶（LC）溶液在玻璃基板上剪切，然后在N2flow下干燥制备薄膜，聚合物链的长轴沿剪切方向分布。在薄膜中，光学显微镜观察到沿剪切方向有条纹状缺陷。在微米（μm）尺度上，这种结构的非均质性有望在微观pATR-FTIR成像获得的分子取向顺序的空间分布图中体现出来。在这项研究中，单轴取向顺序参数S和均方余弦值⟨cos2ψ⟩分别用于量化PI主链和芳香亚胺平面的取向程度。揭示了薄膜在theS的空间分布图中明显是均匀的，而薄膜在⟨cos2ψ⟩的空间分布图中表现出明显的异质性，其中“正面”和“侧面”取向域共存。结果表明，在热亚胺化过程中，刚性PI链的取向方向固定在取向PAE基体的平均取向方向上，而芳香亚胺环可以绕主链旋转。此外，利用ATR-FTIR成像成功地显示了PI膜中的裂纹，并研究了裂纹内的取向分布。通过本结构研究，我们通过对高取向PI薄膜的分析，验证了微pATR-FTIR成像方法的定量能力，并证明了其在分子取向分析基础上研究μm尺度非均质性的能力。
Molecular orientation of aromatic polyimides (PIs) and their precursor of poly(amic ester)s (PAE) in the biaxially oriented films were analyzed by polarized microscopic attenuated-total-reflection Fourier-transform infrared absorption spectroscopy (micro pATR-FTIR) imaging. The films were prepared by shearing a lyotropic liquid crystal (LC) solution of the PAE on a glass substrate and subsequent drying under a N2flow, and the long axis of polymer chains were distributed around the shear direction. In the film, streak-shaped defects were observed along the shear direction with optical microscopy. Such structural heterogeneities on the micrometer (μm) scale are expected to be visualized in spatial distribution map of molecular orientation order acquired with micro pATR-FTIR imaging. In this study, uniaxial orientation order parameter,S, and a mean square cosine value, ⟨cos2ψ⟩, were used to quantify the degree of orientation of the PI main chain and that of aromatic imide plane, respectively. It was revealed that the films are apparently homogeneous in the spatial distribution map of theS, while the films exhibited obvious heterogeneity in that of ⟨cos2ψ⟩, in which “face-on” and “edge-on” orientation domains coexist. The results indicate that orientation direction of the rigid PI chains is fixed in the averaged orientation direction of the oriented PAE matrix during thermal imidization, while the aromatic imide ring can be rotated around the main chain. Furthermore, cracks in the PI film were successfully visualized by ATR-FTIR imaging, and the orientation distribution inside the cracks was investigated. Through this structural study, we validated the quantitative capability of the micro pATR-FTIR imaging method thorough the analyses of highly oriented PI films and demonstrated its ability to investigate μm-scale heterogeneity on the basis of molecular orientation analyses.