聚酰亚胺中吸水性的振动光谱分析及其与10ghz介电性能的关系。

IF 2.9 2区 化学 Q3 CHEMISTRY, PHYSICAL
Ririka Sawada, Haonan Liu, Shinji Ando
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引用次数: 0

摘要

揭示聚酰亚胺(pi)介电性能在高频(GHz)范围内相对湿度(RH)依赖性背后的机制是开发新型低介电热稳定聚合物的关键挑战。本文基于变rh傅里叶变换红外(FT-IR)振动光谱,对15种芳香族和半芳香族pi的介电常数(Dk)、耗散因子(Df)、吸水率和吸附H2O分子的氢键结构之间的相关性进行了精确分析。随着大气相对湿度的增加,PI膜中吸收的H2O分子的O-H伸缩(ν(OH))和H-O-H弯曲(δ(HOH))振动的红外波段吸光度逐渐增加。值得注意的是,Dk和Df的增加相对于δ(HOH) IR波段(a δ(HOH))的积分面积的斜率几乎是恒定的,并且与pi的化学结构无关。δ(HOH) IR波段可以用来衡量吸附水的浓度。然而,Dk和Df的RH依赖性的斜率,即hDk和hDf,强烈依赖于pi的结构,并且彼此成正比。这证实了水分的吸收量是影响Dk和Df相对湿度依赖性的关键因素。在较低的相对湿度下,pi的Dk值随α δ(HOH)的增加呈线性增加,而Df值随α δ(HOH)的增加呈线性增加,但在较高的相对湿度下逐渐呈凹形增加。此外,所有pi的a δ(HOH)和Df之间的关系几乎沿一条主曲线对齐。这种统一而显著的Df增加可能是由水的大Df(~ 0.5)和水分子在PI膜中吸附的塑化作用引起的。这种水诱导的塑化激活了PI链中具有大偶极矩的部分(即亚胺和酯基)的局部弛豫运动,共振频率为10 GHz。此外,红外ν(OH)波段的光谱分解使得在分子水平上对吸附和氢键H2O分子的结构进行分类和表征,即1)H2O分子直接与亚胺羰基(C = O)基团形成氢键(HBs),称为“结合水”,以及2)H2O分子与结合水形成HBs,称为“自结合水”。值得注意的是,随着Aδ(HOH)的增加,自伴生水(Aassoc)的光谱组分总量与Df同时呈曲线增加。Aassoc和Df之间的准线性关系表明,Df随着a δ(HOH)的快速增加,反映了通过水塑化激活PI链局部运动,与自缔合水的数量密切相关。为了降低pi在较高频率下的相对湿度和吸水率对Dk和Df的依赖,有效的策略包括引入疏水氟原子和抑制在同一频率范围内自相关水诱导的局部分子运动。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Vibrational Spectroscopic Analysis of Water Absorption in Polyimides and the Correlation with Dielectric Properties at 10 GHz.

Unveiling the mechanism behind the relative humidity (RH) dependence of the dielectric properties of polyimides (PIs) in the high-frequency (GHz) range is a crucial challenge in the development of novel low-dielectric thermally stable polymers. Herein, the correlations among the dielectric constant (Dk), dissipation factor (Df), water absorption content, and hydrogen-bonding structures of sorbed H2O molecules were precisely analyzed for 15 types of aromatic and semiaromatic PIs based on variable-RH Fourier transform infrared (FT-IR) vibrational spectroscopy. The absorbance of the IR bands assignable to the O-H stretching (ν(OH)) and H-O-H bending (δ(HOH)) vibrations of H2O molecules sorbed in PI films gradually increased with an increase in the RH of the atmosphere. Notably, the slopes of the increase in Dk and Df against the integrated area of the δ(HOH) IR band (Aδ(HOH)), which can be used as a measure of the concentration of sorbed H2O, were nearly constant and independent of the chemical structure of PIs. However, the slopes of the RH dependences of Dk and Df, that is, hDk and hDf, were strongly dependent on the structure of PIs and proportional to each other. This confirms that the amount of water absorbed is a crucial factor in the RH dependence of Dk and Df. The Dk values of the PIs increased linearly with an increase in Aδ(HOH), whereas the Df values increased linearly with Aδ(HOH) at a lower RH but gradually showed a concave-up increase at a higher RH. In addition, the relationship between Aδ(HOH) and Df for all PIs was nearly aligned along a single master curve. This unified and marked increase in Df could be induced by both the large Df of water (∼0.5) and the plasticization effect of the H2O molecules sorbed in the PI films. This water-induced plasticization activates the local relaxation motions of the moieties with large dipole moments, i.e., the imide and ester groups, in the PI chains, resonating at 10 GHz. Furthermore, the spectral decomposition of the IR ν(OH) band enables the classification and characterization of the structures of sorbed and hydrogen bonded H2O molecules at the molecular level, namely 1) H2O molecules directly form hydrogen bonds (HBs) with imide carbonyl (C═O) groups, called "bound water," and 2) H2O molecules form HBs with bound water, called "self-associated water." Notably, with an increase in Aδ(HOH), the total amount of the spectral components of self-associated water (Aassoc) increased curvilinearly and simultaneously with Df. The quasi-linear relationship between Aassoc and Df suggests that a rapid increase in Df with Aδ(HOH), which reflects the activation of the local motion of PI chains via water plasticization, is strongly correlated with the amount of self-associated water. To reduce the dependence of RH and water absorption on Dk and Df of PIs at higher frequencies, effective strategies include the introduction of hydrophobic fluorine atoms and the suppression of self-associated water-induced local molecular motion resonating in the same frequency range.

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来源期刊
CiteScore
5.80
自引率
9.10%
发文量
965
审稿时长
1.6 months
期刊介绍: An essential criterion for acceptance of research articles in the journal is that they provide new physical insight. Please refer to the New Physical Insights virtual issue on what constitutes new physical insight. Manuscripts that are essentially reporting data or applications of data are, in general, not suitable for publication in JPC B.
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