| 摘要: | 石墨烯（graphene）因具有良好的導熱(導熱係數高達5300 W/mK)、載子傳輸速率、機械強度、光穿透率、化學穩定性等特性，進而廣泛地被應用在各個領域上，其優異的熱傳導性質可以解決高分子材料最令人詬病的部分也就是熱性質方面的問題。本實驗將著重於在有機高分子中具有較佳熱安定性的聚亞醯胺(polyimide，PI)，由於運用在電子元件的構裝或是半導體元件製作上，其製程溫度常需高達300℃以上。所以為了改良PI導熱不佳的性質須結合高導熱性質的填充劑，如石墨烯、陶瓷填料等，以期能提升導熱性質。
本論文將採用不同石墨烯，如氧化還原石墨烯(RGO)及電化學石墨烯(ECG)，混合不同結構型態的陶瓷填料，如氧化鋁(Al2O3)、氮化硼(BN)及氧化鎂(MgO)，並進一步探討粒徑大小、填隙率等參數，對於混成製作所得薄膜的導熱性質、表面電阻與薄膜機械性質之影響，以達到高性能PI膜的開發，未來可應用於高導熱、表面高電阻、耐高溫、可彎曲之電子元件、半導體元件製作。研究目標為聚亞醯胺/石墨烯/陶瓷填料之表面電阻維持在高於1011 Ω，且導熱係數>1 W/mK。
本研究總成果顯示： (1)石墨烯C/O比與層數對於導熱值的影響，高C/O比之石墨烯具有較佳的導熱性，而少層相對於多層具有較佳的導熱趨勢； (2)不同型態結構之陶瓷填料與石墨烯相互作用於高分子中，對薄膜機械性質的影響，其結果顯示石墨烯對於球體陶瓷填料，具有更加明顯的機械性質提升，增加薄膜可撓性及韌性，而多層石墨烯對於少層石墨烯能更明顯提升薄膜機械性質。其中在添加氧化鎂之後，薄膜機械性質大幅下降且易脆，但僅添加石墨烯濃度1 wt%之後，即可得具有可撓性之薄膜；(3)添加石墨烯後導熱值提升約1.4倍，目前可得到(i)氧化鋁濃度50 wt%，並添加RGO~2 wt%，可以得到導熱值1.22 W/mK，並同時維持表面高電阻、薄膜完整性且具韌性之薄膜。(ii)高填隙率之氧化鋁在濃度40 wt%，大小粒徑比1：12，並添加RGO~3 wt%，僅能得到導熱值約1.1 W/mK。(iii)氮化硼濃度50 wt%，並添加RGO~2 wt%，可以得到導熱值2.26 W/mK，約提升1.4倍且表面電阻>1011Ω。
除了以導熱係數及表面電阻外，我們另外觀察薄膜機械性質，分為是否為易脆及薄膜完整性之參數。薄膜完整性對於大面積生產具有相當重要的意義，而易脆將不利於其應用性，若是陶瓷填料填充含量過多將導致機械性質下降，而添加石墨烯可以在這之中擔任緩衝層，將其填充至高分子缺陷中，減少孔隙率，增加緻密性，進而提高柔韌性，獲得具有可撓性之薄膜。
本研究結合PI與石墨烯、陶瓷填料等，開發具有高導熱且同時保有表面高電阻，並能夠具有一定機械性質之薄膜。
;Graphene has high mechanical strength and superb thermal conduction property (up to 5300 W/mK), in addition to flexibility, high mobility and optical transparency. Its excellent properties can improve the most repellent part of polymer materials, with regard to thermal properties. In this study, in order to achieve high surface resistance and high thermal conductivity in the polymer composite, various inorganic fillers including alumina (Al2O3), magnesium oxide (MgO) and boron nitride (BN) with different size were used alone or in combination with graphene to achieve thermally conductive and insulating properties. Polyimide (PI)/graphene (Gra)/ceramic powder composites were prepared by solution blending. In the case where the ceramic powder was separately added, the use of hybrid filler was found to be effective in increasing thermal conductivity of the composite. However, as the amount of addition increases, the mechanical strength of as-prepared film were decrease drastically. Therefore, the incorporation of graphene in this work not only increased the thermal conductivity but also enhance their mechanical properties. Multilayer graphene can significantly improve the mechanical properties of the film for few layers of graphene, especially in MgO. This was believed that the graphene additives may serve as buffer materials among PI/ceramics, which can fill the defect, reduce porosity, and increased density, thereby increasing flexibility. Furthermore, the thermal conductivity of composites, with only 2 wt% of Reduced graphene oxide (RGO) as additives, can significantly increase to 2.26 W/mK, approximately a 1.4-fold enhancement when compared with the results obtained using the same concentration of 50 wt% of hBN; the Al2O3 also has the thermal conductivity of about 1.2 W/mK at a concentration of 50 wt% and addition of RGO 2 wt%. The significant improvement in thermal conductivity can be attributed to the generation of effective thermal conductive pathways formed by graphene and various inorganic fillers in the composite. This study will discuss in detail the role of graphene in thermal conductivity and mechanical properties in composites. |
