孤对电子对聚合物修饰碳纳米管吸波性能提高的作用机制

In recent years, the microwave absorbing materials continue to attract considerable interest because of their applications in commercial and military purposes.Extensive studies have been carried out to find suitable microwave absorbers under the development of communication technology.Multi-walled carbon nanotubes (MWNTs), with unique structure and many excellent properties, have potential application for microwave absorption.However, it is widely acknowledged that the exciting properties of MWNTs in polymeric matrix mainly depend on their dispersion and interfacial interaction. Unfortunately, because of their high aspect ratios, large special surface area and substantial van der Waals attractions, MWNTs tend to self-aggregate into bundles. In this study, polymers with different chain composition, chain length and chain shape, such as linear and branched polymer of polyetherimide, polyethylene glycol and polythioether,which all have lone pair electrons, will be synthesized and be chosen as dispersants to modify MWNTs.The modification of MWNTs by polymers with lone pair electrons can prevent MWNTs to aggregate and enhance the dispersibility, which is significant to adjust the dielectric parameter and enhance the microwave absorbing properties.On the other hand, the lone pair electrons can interact with MWNTs π-electrons to increase the polarization degrees of MWNTs,which is more important to enhance the dielectric parameter and microwave absorbing properties.The effect of the chain composition, chain length and chain shape on the electric field intensity of polymers will be investigated.The effect of the chain composition, chain length and chain shape of polymers on the morphology of MWNTs will be investigated. The effect of the chain length,chain composition and chain shape of polymers on the improved conductivity will be studied. The effect of the electron density and distribution on polarization degrees, dielectric parameter and enhanced dielectric losses of MWNTs will be measured. The mechanism of the lone pair electrons on the improved absorbing properties of MWNTs modified by polymers will be studied, which is more important to develop a kind of new microwave absorbers.

聚合物修饰纳米碳管(MWNTs)可以提高吸波性能，而含孤对电子聚合物修饰碳纳米管会使效果更为显著，但其具体作用机理并不清楚。含孤对电子聚合物修饰MWNTs，既改善碳纳米管π电子的均匀分散，又与碳纳米管π电子作用，影响MWNTs的极化程度，因此研究孤对电子与碳纳米管π电子的相互作用将为提高吸波性能提供理论依据，但这方面研究鲜有报道，亟待深入研究。基于此，本项目设计合成不同链段组成、不同链长及链形状含孤对电子的聚乙烯酰亚胺（PEI）、聚乙二醇（PEG）以及聚硫醚（PES），并通过溶液共混超声分散非共价包覆修饰MWNTs，研究聚合物链段组成、链长及链形状对MWNTs微观形貌、聚集形态、包覆层尺寸等影响，阐明链段组成、链长及链形状对聚合物微电场强度、MWNTs极化程度及电磁参数的影响规律，揭示孤对电子对聚合物修饰MWNTs吸波特性提高的作用机理，为发展新的微波吸收材料奠定理论基础。

聚合物修饰碳纳米管（MWNTs）可以提高吸波性能，而含孤对电子聚合物修饰会使效果更为显著，但其作用机理尚未清楚。本文采用含孤对电子聚合物(PVA、PMMA、PVP、PEI、PEG等）非共价修饰MWNTs，探讨了孤对电子对聚合物修饰多壁MWNTs分散性、微观形态和吸波性能的影响。采用红外光谱、拉曼光谱、扫描电镜、透射电镜、矢量网络仪等手段表征了修饰前后MWNTs表面形貌、分散性、介电性能和吸波性能。结果表明经聚合物PMMA修饰后，MWNTs仍然保持原有分子结构特征。修饰后MWNTs分散性变好，缠绕、团聚现象减轻；对比分析了含O聚合物（PMMA）和含N聚合物（PVP）对MWNTs吸波性能的影响。在相同添加量（11wt.%）的情况下， PMMA/MWNTs在8.8GHz处有最大反射损耗-37dB，损耗小于-10dB的频宽为2.1GHz；而PVP/MWNTs在7.8GHz处有最大反射损耗-24.7dB。分析研究了聚合物分子量（PVP）对包覆修饰MWNTs吸波性能的影响。结果表明，随着PVP分子量增大，吸波强度和吸收频宽都有十分明显的增加；当PVP分子量为25860时吸波最好，最大吸波强度-31.16dB（11.9GHz）；同时发现当分子量增大后，其最佳吸波峰的位置向高频处发生移动。研究了聚合物（PEG）用量对MWNTs的影响，当PEG含量7%时吸波最佳，最大反射损耗-25.2dB（10.2GHz）。探索了聚合物构型（线型PMMA和星型PMMA）对MWNTs极化程度吸波性能的影响规律。星型PMMA/MWNTs在9.0GHz处达到最大吸波强度-45.0dB,线性PMMA/MWNTs在8.8GHz处达到最大吸波强度-37.0dB。采用聚乙烯醇（PVA）和聚乙二醇（PEG）修饰MWNTs，研究了聚合物链上孤对电子位置对MWNTs吸波性能影响。当聚合物含量为7%时， PVA/MWNTs在10.7GHz处吸波性能高达-30.6dB，而PEG/MWNTs在10.2GHz处反射损耗为-25.2GHz。本课题研究了聚合物链组成、链长、链形状，聚合物用量以及聚合物链上孤对电子位置对MWNTs微观形貌、聚集形态、MWNTs极化程度及电磁参数的影响规律，揭示了孤对电子对聚合物修饰MWNTs吸波特性提高的作用机理。以上研究可为寻求新一代微波吸收奠定理论基础。