單根奈米纖維之熱傳導率

Abstract

本論文主要在研究單根奈米纖維之熱傳導率，之前的研究顯示聚乙烯在超拉伸之後形成之奈米纖維，其熱傳導率大幅高於其塊材之值，其原因為在拉伸時造成晶格的重組，造成分子鍊的順向性，我們在此研究中使用之奈米纖維為尼龍-6(Nylon 6)，尼龍-6與聚乙烯的相似處是結構簡單，故我們認為其奈米纖維有與聚乙烯相同之熱傳增強特性，在此研究中，我們應用微機電製程製作一微元件，並設計一可控制溫度之真空系統，利用靜電紡絲法製作奈米纖維，同時研究此奈米纖維之熱傳導率。目前我們發現從30 K至130 K，熱傳導率是緩慢上升的情形，至130 K時達到一高峰值，而從130 K至190 K，熱傳導率則是急速下降，190 K到380 K則是平緩趨近於0.2 W/m-K，而在130 K時，其熱傳導率的高峰值為3.34 W/m-K，這個值是尼龍-6在塊材之值的10倍，而在130 K時的高峰值，以及熱傳導率在這個溫度由上升轉變為下降的趨勢目前尚未有文獻提出。

This study aims to investigate the thermal conductivity of a single polymer nanofiber. It has been shown that an ultra-drawn polyethylene nanofiber has a thermal conductivity much large than its bulk value. The thermal conductivity enhancement in the nanofiber was attributed to the lattice-reconstructing during an ultra-drawing process. As a result, most chains are aligned in the nanofiber after the ultra-drawing process as compared to randomly oriented in the bulk, resulting in an enhanced thermal transport. In this study, the thermal conductivity of a single nylon 6 nanofiber was investigated. The bulk nylon 6 has a simple molecular structure as that in polyethylene and the hydrogen bonds could be formed between the polymer chains in the fiber. Thus, it is expected that it might exhibit similar thermal conductivity enhancement during the nano-structuring process. A micro-device has been made to measure the thermal conductivity of a single nylon 6 nanofiber. The nylon 6 nanofibers were electrospun on the fabricated microdevices. It was found that the thermal conductivity of the nanofiber increase with temperature and reaches a peak value of 3.34 W/m-K at 130 K. There has a sharp transition of the thermal conductivity of the nanofiber at 130 K. The thermal conductivity starts to decrease with temperature after this point and it saturates at 0.2 W/m-K after 190 K.