基於醣類高分子/奈米碳管複合材料 之界面工程於熱電應用

Abstract

熱電材料能夠將廢熱直接轉換為電能，是綠色能源技術中極具發展潛力的研究領域。近年來，奈米碳管（CNTs）及其奈米複合材料，因具備優異的熱電性能、優良的機械強度與獨特的物理化學性質，已被廣泛認可為具前瞻性的熱電材料候選者。然而，CNTs 在溶液中易產生聚集現象，限制其在材料中的均勻分散與電荷傳輸效率。為改善此問題，本研究引入醣基結構的高分子作為分散劑，藉由分子間作用力提升 CNTs 在溶液中的穩定分散性，進而促進奈米複合材料中連續且高效導電通道的構建，對提升整體熱電性能具有關鍵性意義。此策略有望推動高效能熱電材料的設計，並為再生能源轉換技術提供可行性方案。 本研究的第一部分聚焦於奈米碳管系統中，導入兩種具有不同寡醣鏈段與苯乙烯（polystyrene, PS）鏈段長度的醣類嵌段共聚物（BCPs），分別為 maltotriose-block-polystyrene（MT-PS）與 maltoheptaose-block-polystyrene（MH-PS），以系統性探討其對奈米碳管分散性與熱電性能之影響。由於這些醣類嵌段共聚物具備明顯的雙親性，其親水性寡醣鏈段可與極性溶劑產生良好互溶性，疏水性苯乙烯鏈段則有助於與奈米碳管表面產生 π–π 作用力，從而實現奈米碳管在 N-甲基吡咯烷酮（NMP）與 N,N-二甲基甲醯胺（DMF）等極性溶劑中的穩定分散。透過溶劑選擇與製程過程的控制，可有效調變複合材料的導電特性，進一步構築具有 p 型與 n 型行為的奈米熱電複合材料。經過製程條件的優化後，所得材料展現出優異的熱電性能，其中 p 型與 n 型複合薄膜分別達到9.10 × 10-3 和 8.78 × 10-3的熱電優值（zT）。此結果也展現出溶劑與材料間相互作用的重要性，以提升奈米複合材料熱電效率。 有別於前述基於物理吸附之分散策略，本研究的第二部分成功合成具醣類官能基的奈米碳管，可穩定分散於水相溶劑中並首次報導應用於熱電材料系統。針對以 maltotriose（MT）與 maltoheptaose（MH）為主體的醣類高分子所官能化之奈米碳管進行系統性探討，結果顯示醣類鏈段在提升分散穩定性與改善熱電性能方面扮演關鍵角色。由於醣鏈中富含羥基基團，能與水溶劑形成氫鍵作用力，顯著提高奈米碳管於水相中的穩定性。另一方面，碳管表面的醣類分子亦有助於降低其熱傳導特性，使官能化奈米碳管之熱導率降低至未修飾奈米碳管的約四分之一。儘管表面修飾導致導電性略有下降，整體熱電性能仍因顯著降低熱導率而獲得提升。在所有樣品中，以 MH 官能基化之奈米碳管（CNT-MH）展現最高熱電優值達 1.46 × 10-3，優於未修飾 CNT 於水相中的表現。上述成果不僅驗證醣類高分子修飾策略在提升熱電效能上的可行性，更提供一項具備永續性、高可調性與溶液製程相容性的界面工程方法，對未來綠色熱電材料之設計與應用具有重要意義。

Organic thermoelectric materials represent a promising frontier in sustainable energy technology, offering the ability to convert waste heat directly into electricity. Among them, carbon nanotubes (CNTs) and their nanocomposites have emerged as strong candidates due to their high thermoelectric performance, exceptional mechanical properties, and unique physicochemical characteristics. In this study, sugar-based polymers are utilized to enhance the dispersibility of CNTs, thereby promoting the formation of efficient conductive pathways within the nanocomposites and contributing to the development of more sustainable energy harvesting technologies. In the first part of this research, two sugar-based block copolymers (BCPs), maltotriose-block-polystyrene (MT-PS) and maltoheptaose-block-polystyrene (MH-PS), featuring varying oligosaccharide and polystyrene block lengths, were synthesized and characterized to investigate their influence on CNT dispersibility and subsequent thermoelectric properties. The inherent amphiphilic characteristics of these BCPs enable efficient dispersion of CNTs in both N-methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF). These solvents prove instrumental in the fabrication of BCP/CNT thin films, yielding both p-type and n-type nanocomposites. Through optimization of processing conditions, the resultant nanohybrids exhibit enhanced thermoelectric properties, with figure of merit (zT) reaching 9.10 × 10-3 and 8.78 × 10-3 for p-type and n-type materials, respectively. Distinct from the aforementioned physical adsorption approach, the second part of this study presents the first report of a stable aqueous suspension of sugar-functionalized CNTs applied to thermoelectric. A systematic investigation of bio-based materials, maltotriose (MT) and maltoheptaose (MH)-based CNTs, reveals that the sugar polymer plays a crucial role in governing both dispersion stability and thermoelectric performance. The multiple hydroxyl groups present in the oligosaccharide segments facilitate strong hydrogen bonding with aqueous solvent, significantly improving the colloidal stability of the functionalized CNTs. Furthermore, the anchored sugar chains on the CNT surface result in a four-fold reduction in thermal conductivity, which outweighs the electrical penalty and contributes to an overall improvement. Sugar-functionalized CNT-MH exhibits the highest zT value of 1.46 × 10-3, outperforming pristine CNTs in aqueous media. Overall, this study offers a versatile and sustainable platform for engineering CNT interfaces in solution-processable thermoelectric systems.