奈米碳管-高分子複合材之無線電頻率電磁波吸收研究

Electromagnetic absorption by carbon nanotube-polymer composites at radiofrequency

秦威(Chin, Wei)

指導教授 ： 徐文光

國立清華大學/工學院/材料科學工程學系/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00647

摘要

In this work, arrays of aligned CNTs are grown and subsequently concreted with parylene to form composites. Such a system made from CNT and polymer displays a linear dichroism in response to incident RF radiation and is supported by differentiated absorbance between longitudinal and transverse directions. For example, the absorption reaches 99% as electric field oscillates along nanotubes and drops below 5% in normal to tube axis; the estimated absorption being 30-60% for randomly arranged CNTs. Origin of enhanced absorptivity at longitudinal direction is analyzed and found related to field induced intra-band transitions within sp2 hybridized orbits. This is supported by ab-initio calculations.

關鍵字

奈米碳管 ； 電磁波吸

並列摘要

此篇論文的內容在探討利用有序排列的多壁奈米碳管(aligned CNTs) 和聚乙烯醇(PVA)所製作的複合材料進行無線電頻率(radiofrequency)範圍內的電磁波吸收實驗。在此實驗中發現，當多壁奈米碳管的排列方向(碳管的長軸方向)相對於電磁波電場振盪方向改變時，複合材吸收電磁波的能力也會隨著改變。當碳管的排列方向和電場振盪方向平行時，複合材電磁波吸收率(absorption)可達99%，但當碳管的排列方向和電場振盪方向垂直時，複合材電磁波吸收率僅為5%,如果使用多壁奈米碳管散亂分散於聚乙烯醇的複合材進行相同的實驗，其電磁波吸收率為30-60%。於此實驗所觀察到的電磁波吸收異向性是由於奈米碳管上未成對電子在電場的作用下於sp2 混成軌域內進行能量躍遷(intra-band transitions)所造成的現象。此現象可以經由ab-initio 理論計算而得到證明。

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