隨著高功率電子元件、高效能運算與5G通訊技術的快速發展，電子裝置在操作過程中產生的局部熱累積問題日益嚴重。因此，開發兼具良好導熱能力、結構穩定性之熱管理材料，已成為提升電子元件可靠度與使用壽命的重要課題。碳奈米管（carbon nanotubes， CNTs） 具有高熱導率 (3500 W/m•K)、高長徑比與良好的網路形成能力，可作為有效的導熱路徑；然而，CNT形成連續網路時亦會造成較高的電導率，限制其於需電氣絕緣之電子元件中的應用。相較之下，六方氮化硼（hexagonal boron nitride， h-BN）具有高面內熱導率（300-600 W/m•K）、優異熱穩定性與電氣絕緣性，適合用於降低碳基材料的導電性並改善熱管理性能。 本研究以真空過濾法製備無黏結劑 CNT/BN 複合紙，並探討 CNT 管徑、CNT/BN 重量比例及壓製處理對複合紙結構、形貌、電性與熱性能之影響。實驗中使用兩種不同管徑之多壁碳奈米管，分別為10–20 nm 與40–60 nm，並固定CNT與BN總重量為150 mg，製備不同CNT/BN重量比例之複合紙。 電導率測試結果顯示，在相同 CNT/BN 重量比例下，10-20 nm小管徑CNT系列之電導率皆高於 40-60 nm 大管徑CNT系列。然而，即使加入BN後，複合紙的最低電導率仍為 12.60 S/cm，說明單純以 CNT 與 BN 均勻混合的方式，仍不足以完全阻斷 CNT 所形成的連續導電路徑。 另一方面，本研究利用Molten Alkali-assisted Exfoliation方法成功製備氮化硼奈米片(boron nitride nanosheets， BNNS)。進一步透過逐層真空過濾法製備 BNNS/CNT/BNNS 三明治結構複合膜，使中間CNT導電網路被上下BNNS絕緣層包覆，進而達到電氣絕緣並抑制表面導電路徑，同時維持材料內部熱傳路徑。 熱導率分析結果顯示，BN的加入有助於提升複合膜的熱傳導能力，在相同 CNT/BN重量比例下，L-CNT/BN複合膜大多具有較高熱導率。於所有樣品中，BNNS/CNT/BNNS 三明治結構之45:60:45樣品具有最高熱導率，達79.34 W/m•K。綜合而言，BNNS/CNT/BNNS 三明治結構可藉由 BNNS 絕緣層包覆 CNT 導電網路，使材料達到電氣絕緣，同時維持良好熱傳能力本研究可作為無黏結劑 CNT/BN 複合紙應用於熱管理與熱介面材料之結構設計基礎。;With the rapid development of high-power electronic devices， high-performance computing， and 5G communication technologies， heat accumulation during device operation has become increasingly severe. Therefore， developing thermal management materials with good heat dissipation capability and structural stability has become an important issue for improving the reliability and lifetime of electronic components. Carbon nanotubes (CNTs) possess high thermal conductivity of approximately 3500 W/m•K， a high aspect ratio， and excellent network-forming ability， allowing them to serve as effective heat-conduction pathways. However， when CNTs form a continuous network， they also result in high electrical conductivity， which limits their application in electronic devices requiring electrical insulation. In contrast， hexagonal boron nitride (h-BN) exhibits high in-plane thermal conductivity of 300-600 W/m•K， excellent thermal stability， and electrical insulating properties， making it suitable for reducing the electrical conductivity of carbon-based materials while improving thermal management performance.
In this study， binder-free CNT/BN composite papers were fabricated using a vacuum filtration method. The effects of CNT diameter， CNT/BN weight ratio， and compression treatment on the structure， morphology， electrical properties， and thermal performance of the composite papers were investigated. Two different diameters of multi-walled carbon nanotubes， 10–20 nm and 40–60 nm， were used， and the total weight of CNT and BN was fixed at 150 mg to prepare composite papers with different CNT/BN weight ratios. The electrical conductivity results showed that， under the same CNT/BN weight ratio， the 10–20 nm small-diameter CNT series exhibited higher electrical conductivity than the 40–60 nm large-diameter CNT series. However， even after the incorporation of BN， the lowest electrical conductivity of the composite papers remained 12.60 S/cm， indicating that simple uniform mixing of CNT and BN was insufficient to completely block the continuous conductive pathways formed by CNTs.
In addition， boron nitride nanosheets (BNNS) were successfully prepared using a molten alkali-assisted exfoliation method. BNNS/CNT/BNNS sandwich-structured composite films were further fabricated through a layer-by-layer vacuum filtration method. In this structure， the middle CNT conductive network was enclosed by the upper and lower BNNS insulating layers， allowing the material to achieve electrical insulation and suppress surface conductive pathways while maintaining internal heat-transfer pathways.
The thermal conductivity results showed that the incorporation of BN enhanced the heat-transfer capability of the composite films. Under the same CNT/BN weight ratio， the L-CNT/BN composite films generally exhibited higher thermal conductivity. Among all samples， the BNNS/CNT/BNNS sandwich-structured film with a 45:60:45 ratio exhibited the highest thermal conductivity， reaching 79.34 W/m•K. Overall， the BNNS/CNT/BNNS sandwich structure can achieve electrical insulation by enclosing the CNT conductive network with BNNS insulating layers while maintaining good thermal transport capability. This study provides a structural design basis for the application of binder-free CNT/BN composite papers in thermal management and thermal interface materials.
