奈米碳管/高分子之微波熔接特性與其應用

Microwave welding of MWNT to polymers and its implications

王智永(Chih-yung Wang)

指導教授 ： 金重勳

國立清華大學/工學院/材料科學工程學系/博士(2007年)

摘要

自1991奈米碳管被發現以來，其優良的機械、導電、導熱及化學反應均廣泛的被研究及應用在各類領域之中。在各類應用中，奈米碳管/高分子的複合材的開發亦廣受矚目，將奈米碳管的優異性質應用在高分子基材上，形成軟性電子元件，為目前的研究主流。傳統製作奈米碳管/高分子複合材的方法大都是以熱熔法將碳管與複合材做均勻混和分散，或以黏結劑將碳管黏著在高分子基材上。前者需要高溫製程將高分子熔解，且高分子/碳管間需具備高的介面親和性。後者則需要以接著劑進行黏結、固化。兩種方法均需較長的製作時間，同時容易產生分散不均、接著強度不佳、韌性不足等問題。微波加熱具有超距、快速、材料選擇性、體積加熱、效率佳等特性。過去很多研究都指出微波對奈米碳管之反應影響，但多集中在頻率響應、共振等電磁特性上，少有討論其微波加熱效果。
本研究的目標分為兩階段，首先是研究多壁奈米碳管的微波加熱特性。實驗中以2.45GHz微波系統加熱多壁奈米碳管證實可使達到900度C以上高溫，再以微波加熱理論探討其微波升溫的機制，及微波加熱後碳管的相關反應。研究確認碳管的微波加熱主要是由於電導損耗的貢獻。利用碳管的瞬間加熱特性，本研究開發了新的奈米碳管/高分子接著製程，稱為「微波熔接」。將碳管分散在高分子基材上，利用微波瞬間加熱數秒鐘，由於碳管的高微波加熱特性，及碳管/高分子兩者間的熱導障礙，碳管釋放的巨熱會瞬間熔融高分子表面，將碳管熔接於高分子上，同時保持高分子基材的完整性。由於是單純的物理性熔接，因此可應用於多類高分子基材如PET、PP、Teflon等。本研究以剝離試驗進行微波熔接之碳管/高分子接著強度的探討，證實其接著強度較傳統黏結劑高達數百倍，同時我們亦研究出利用應力轉移的方式，可使碳管順向排列，有機會應用於異向碳管膜的製作。
本研究的第二階段是利用微波熔接製程，搭配碳管膠的製作及印刷技術，進行多類可撓曲式軟性電子製作，如可撓曲的單面電阻體、導體及場發射體。以微波熔接製作的軟性電子材不僅碳管耗量少、製程時間快、重要的是可充分展現碳管的優異特性，如高導電性、場發射性質等，而不被傳統製程中的黏結劑所影響，亦不影響高分子基板本身的機械特性，碳管/高分子間足夠的接著強度亦使得其可在撓曲狀態依然維持其相關特性。
最後，本研究提出後續研究工作，微波熔接或是微波的相關特性，除了多壁奈米碳管的相關研究，亦可利用於其他材料的相關研究上，其反應特性及其特殊的元件特性均是未來值得研究的重點。

關鍵字

奈米碳管 ； 微波加熱 ； 微波熔接 ； 可撓曲 ； 場發射

並列摘要

Since the discovery of carbon nanotubes (CNTs) in 1991, there had been a huge number of investigations on its basic properties and applications. Superior properties have been found such as high electric and thermal conductivity, mechanical strength, low threshold voltage for field emission, among many others. Nowadays, CNT/polymer composite gains much attention due to its industrial development especially for flexible electronics. The general access to CNT/polymer composite has been studied such as melt-mixing, spinning, in-situ polymerization and adhesive. Among these, the unavoidable problem was that the poor adhesion between CNT/polymer or the thermal deformation of substrate. On the other hand, microwave is a kind of specific energy that could transfer energy directly to materials via molecular interactions. The unique characteristics of microwave heating such as remotely, quickly, volumetric and material-selective make it much suitable for solving the adhesion problem of CNT/polymer.
In this study, we first successfully examined the microwave heating of multi-wall carbon nanotube (MWNT) while the maximum temperature could be higher than 900 oC and made clear the heating mechanism. By such characteristic, MWNT can be easily bonded onto polymer substrates under microwave irradiation within a few seconds which we developed and called it microwave welding process. It was shown that the MWNTs are good ‘solders’ of polymer parts with a strength two orders of magnitude higher than those bonded by adhesives.
The other study was focused on the implication of microwave welding. The microwave welding is a new access to flexible electronic companying with the paste-printing technique. There is no more interlayer such epoxy necessary in MWNT/polymer composite and the MWNT welded on polymer’s surface could fully exhibit its superior properties such electron conduction, field-emission. The flexible device would exhibit better than traditional way due to the strong surface welding without crack or deformation within polymer substrates. Finally, for more rapidly, uniformly and selectively heating characteristics, microwave welding was demonstrated to be of great importance in flexible electronics, such as conductors, resistors and field emitters.

並列關鍵字

carbon nanotube ； microwave heating ； microwave welding ； flexible ； field emission

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