- 學位論文
導電高分子化學氣體感測器
Chemical Vapor Sensors Fabricated from Conducting Polymers
摘要
偵測化學氣體的目的為收集生物體或周圍環境的資訊以利決策，近年來隨著對環境保護及人類健康的意識持續抬頭，化學氣體感測器受到多方的重視，包括製造工人、實驗室人員、醫療專家、食品製造者及一般家庭等等。然而，能夠精確、具選擇性的化學氣體感測，尤其是對使用者友善且不受水氣干擾的感測方法仍然未被實現。導電高分子的性質可以藉由化學結構、表面形貌和化學氣體來調控，因而被視為具高度潛力的感測材料。 本論文的主旨在於了解高分子化學結構和薄膜的表面形貌，對於偵測待測氣體和開發高靈敏感測器的影響，偵測氣體包含胺類、芳香烴碳氫化合物、氯化物和酮類。導電高分子的化學結構和薄膜表面形貌會影響其光學及電學性質，因此利用導電高分子製備出光學感測器和電性感測器，來偵測不同種類的化學氣體，因為不同種類的氣體有各自合適的量測方法。 在光學感測器的部分，利用導電高分子∕奈米粒子混摻薄膜的光學性質變化，來偵測化學氣體的存在，該薄膜的光學性質與其奈米級形貌有深度關聯，而奈米形貌又非常容易受到特定化學氣體之影響，因此我們得以判斷該氣體的存在與否。所設計的混摻薄膜不受到水起干擾，且對有機芳香烴尤為敏感，在1%下的苯—甲苯—二甲苯混合物或汽油燃料都能及時反應。此新穎的感測機制可以廣泛地用於爆炸性化學物質的洩漏上。開發的感測晶片搭配一個真正感測器，在實地測試中成功偵測到環境中的化學氣體。 在電性感測器的部分，利用噻吩—異靛藍素予體—受體導電高分子製作出的電晶體，來感測胺類和酮類，這種高分子具有簡易合成方式、空氣下優異的載子傳輸等優點。在本論文中著重於表面形貌、官能基與比表面積的影響。對於表面形貌，本論文中研究了高分子化學結構的差異、表面形態的控制和氨氣感測器的表現之關係，結果顯示對於增加高分子受氣體影響的傾向而言，高分子薄膜必須擁有高結晶度、側向高分子結晶排列與直接的氣體滲透通路。對於官能基，本論文利用含氟官能基來提升氣體感測器的靈敏度，因為含氟官能基可與待測氣體直接作用。偵測器的靈敏度取決於高分子的化學結構與待測物的特性，例如，像胺類的高極性分子能夠透過與高分子中的氟原子產生氫鍵，而更緊密地吸附在載子通道上，來大幅增加偵測靈敏度；而丙酮、二甲苯等化學氣體僅經由偶極作用力和凡得瓦力與高分子作用，故需要在高分子或介電層表面累積較多的氣體分子後，才能達到與胺類相當的反應程度。對於比表面積，本論文提出一種便捷且可普遍適用的合成方式，在不須要透過使用模板的情況下，來製備具奈米結構的導電高分子薄膜，這個簡便的方法使用超分枝高分子當作添加劑，以調整導電高分子表面形貌為連續網狀奈米纖維。具奈米結構的導電高分子薄膜具有更高的結晶度，因此有良好的電荷載子傳輸能力及穩定的網狀奈米纖維結構，而在移除添加劑時不會犧牲這兩種性質。藉由結合化學結構、表面形貌、比表面積和奈米結構，氟化異靛藍素予體—受體導電高分子電晶體能夠在數秒內偵測ppb等級的氨氣。 對化學氣體感測而言，導電高分子是非常有潛力的材料，本論文在光學和電性感測器兩方面展現了此種材料在感測的能力。本論文系統性地研究化學結構和表面形貌對於提升導電高分子—待測分子作用力的影響：在光學感測器方面，藉由溶劑效應、支鏈效應和溶解度效應來探討高分子鏈在混摻薄膜中的動力學；在高分子場效電晶體方面，著重在許多關鍵要素上，如高分子的結構、官能基、結晶排列規整度以及表面形貌。此篇論文的研究結果在導電高分子的基礎性質與其和化學氣體之間的交互作用方面提供許多見解，希望這些發現和建立的方法能夠讓高分子材料的開發有所進展，並能在感測器及其他應用上有所貢獻。
並列摘要
The aim of detecting chemical vapors is to gather chemical information on living beings or surrounding environments for further decision making. With the increasing concerns for environments and the growing awareness of human health, the detection of chemical vapors is of great interest to many, including but not limit to manufacturing workers, laboratory personnel, medical specialists, food providers and common households. However, precise and selective detection of chemical vapors has yet been realized in user-friendly sensing techniques without interference of moisture. Conducting polymers are promising materials for sensors since their properties can be tuned by chemical structures, morphology and chemical vapors. This dissertation aims to understand the effect of chemical structure and morphology on detecting analytes and develop highly sensitive sensors to detect amines, aromatic hydrocarbons, chlorides and ketones. The chemical structure and morphology of conducting polymers lead to different optical and electrical properties. Optical and electrical sensors made from conducting polymers are both explored in detecting chemical vapors since different chemical vapors are better detected by different sensing methods. In the section of optical sensors, conducting polymers/nanoparticles blend films are utilized to detect chemical vapors via the induced changes in optical properties. The absorption of blend films are closely related to the morphology of films and the aggregation of polymers, which can be tuned by chemical vapors. The solvent effect and side chain effect of conducting polymers are given special focus to tune the nanomorphology of blend films and their susceptibility to chemical vapors. The designed blend films are free from the interference of moisture and particularly sensitive to aromatic hydrocarbons and chlorides. Instant responses have been achieved upon exposure to 1% mixture of benzene, toluene and xylene (BTX) or gasoline fuels. The novel sensing mechanism can be widely utilized in the leakage of explosive chemicals. A sensor device equipped with the developed sensor chip can successfully detect the presence of chemical vapors on field. In the section of electrical sensors, field-effect transistors (FETs) made from thiophene-isoindigo donor-acceptor conducting polymers are used to detect amines and ketones. These polymers have advantages of simple synthesis and excellent charge transport in air. This dissertation focuses on the influence of morphology, functionality and surface area. For morphology, the relationship among chemical structures, morphology control of the conducting polymers and the performance of ammonia sensor is investigated. High crystallinity, edge-on polymer packing orientation and direct percolation routes for analytes are found to be essential to increase the susceptibility of polymer films to analytes. For functionality, fluorine functional group is explored to enhance sensitivity due to the potentially direct interaction with analytes. Polar molecules such as amines with potential hydrogen bond donor can adsorb in close vicinity to conducting channels due to the formation of hydrogen bond with fluorine atoms, enhancing the sensitivity significantly. Chemical vapors such as acetone and xylene interacting with the polymers via dipolar or van der Waal forces have to accumulate sufficient amounts in the polymer films or at the dielectric interface. As for surface area, a general and facile synthesis has been developed to prepare nanostructured conducting polymer films without hustles of using templates. The simple approach employs hyperbranched polymer as additive to tune the morphology of conducting polymer film into continuous nanofibril network. Nanostructured conducting polymer films with improved crystallinity exhibit good charge carrier transport and stable nanofibril network without sacrificing either property when removing residual additives. By combination of chemical structure, morphology, surface area and nanostructure, fluorinated donor‒acceptor isoindigo polymer transistor can detect the ammonia down to ppb range in few seconds. Chemical vapor sensing using conducting polymers is demonstrated in the form of optical and electrical sensors. High sensitivity sensors can be achieved by tuning chemical structure and morphology to promote the interaction between polymer and analyte by varying solvent, side chain, additive and so on. The effects of each parameter have been systematically carried out. The results in this dissertation provide insights to fundamental principles of conducting polymers and their interaction with chemical vapors. It is our hope that these findings and established methods can advance the polymeric materials development for sensors and other applications.