Preparation and Characterization of Polypyrrole/Carbon Nanotubes Composites Using Polyelectrolytes

聚吡咯(polypyrrole, PPy)為常見的本質型導電高分子，因具有製程容易與環境穩定性等優點，因此，被廣泛應用於感測器、電子元件和電容等方面。依照不同的製備方法，其摻雜程度亦不同，所製備之聚吡咯導電度也會有所不同，一般介於10-3~102 S/cm之間。但由於聚吡咯之溶解度、加工性及機械性質皆不佳，因此大大降低其應用面。在本研究中，藉由奈米碳管優異的電性、熱性質以及機械性質等，與聚吡咯形成複合材料，進而改善聚吡咯之缺點。 為了使奈米碳管在高分子基材中達到良好的分散性，又不會破壞其原始特性，本研究採用非共價鍵結表面改質的方式來進行奈米碳管之分散，研究中以陰離子型聚電解質，Poly(Sodium 4-Styrenesulfonate) (PSS)，為奈米碳管分散劑。利用PSS於水溶液中以靜電吸附的方式纏繞著奈米碳管，使其在水溶液中有良好的分散，再加入吡咯單體，同時PSS也可作為聚吡咯之摻雜劑的角色，以化學原位聚合法製備聚吡咯/奈米碳管複合材料，並對其性質作進一步的研究與探討。 當PSS濃度由1 mg/ml提高至3 mg/ml時，所製備之聚吡咯顆粒大小由50-70 nm縮小至30-50 nm。經由XRD分析結果得知，PSS製備之聚吡咯皆為非晶結構。而FTIR、Raman、UV-visible光譜以及元素成分分析結果顯示，在聚吡咯聚合過程中，PSS扮演摻雜劑的角色，且隨PSS濃度的增加，所製備聚吡咯之摻雜程度也愈高。當PSS濃度為2.5 mg/ml時，所製備之聚吡咯有最佳導電度~150 S/cm。此外，隨著PSS濃度增加，聚吡咯熱穩定性也隨之提升。進一步導入奈米碳管形成聚吡咯/奈米碳管複合材料後，由FE-SEM及TEM觀察可知，其表面形態除了聚吡咯顆粒聚集外，奈米碳管表面有聚吡咯層的披覆，形成「核-殼結構」。FTIR、Raman、UV-vis光譜分析透露PSS同時扮演著摻雜劑的角色，且隨著PSS濃度增加，其複合材料摻雜程度也隨之提升。當PSS濃度為5 mg/ml時，聚吡咯/奈米碳管複合材料有最佳的導電度值約90 S/cm，且為純聚吡咯/奈米碳管複合材料導電度的2~3倍。EPR結果顯示，在PSS濃度為5 mg/ml時，所製備之複合材料有最高的自由電子數目，且EPR之曲線與導電度趨勢相吻合。 另一方面，改變吡咯單體含量之聚吡咯/奈米碳管複合材料中，由FE-SEM觀察得知，隨著吡咯單體含量增加，愈不易發現裸露的奈米碳管，是由於奈米碳管表面被聚吡咯披覆所致。而導電度隨吡咯單體含量增加呈現上升-下降-上升的趨勢，當PSS : pyrrole weight ratio=1:2時，有最高的導電度值，約90 S/cm。由TGA結果得知，當吡咯單體含量愈少，所製備之聚吡咯/奈米碳管複合材料的熱穩定性則增加。然而，改變奈米碳管添加量之聚吡咯/奈米碳管複合材料中，由XRD結果顯示，奈米碳管添加量超過3 wt%時，可稍微發現奈米碳管2θ=26°時，(002)結晶面的主要繞射峰。導電度方面則呈現一個範圍的跳動，並沒有因為奈米碳管添加量上升，使複合材料的導電度上升；推測是由於純奈米碳管的導電度沒有摻雜後的聚吡咯高，故無法有效提升複合材料的導電度，另一方面，可能是由於PSS對導電度的影響遠大於奈米碳管。EPR結果顯示，奈米碳管添加量愈多，其複合材料之自由電子數目呈現減少的趨勢，但其變化仍不大，此與導電度變化有些微吻合。由TGA結果表示，隨著奈米碳管添加量增加，聚吡咯/奈米碳管複合材料之熱穩定性也隨之提升。Polypyrrole (PPy), one of the most widely used intrinsic conducting polymers, can be applied in many aspects such as sensor, electronic device and capacitor due to its relative ease of synthesis and environmental stability. The conductivity of polypyrrole is dependent on the fabrication method and doping level, which is normally in the range of 10-3~102 S/cm. But there are some limitation for processing polypyrrole owing to its poor solubility and mechanical property. In this study, we have prepared polypyrrole/carbon nanotube composites by using excellent properties of carbon nanotubes (CNTs) to improve the drawbacks of polypyrrole. In order to improve the solubility of the CNTs in solution without any structural damage, the surface-modified approach with noncovalent bond is considered. Anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS), used as modifier was applied to overcome the difficulty of CNT's dispersion into insoluble and infusible polymer matrix. First CNTs were initially dispersed in water in the presence of PSS acted as the wrapping polymer through electrostatic interactions under sonication. Then pyrrole was polymerized by in-situ chemical oxidative polymerization on the surface of the CNTs. At the same time, PSS can also be acted as the dopant of polypyrrole. The morphology and physical properties of fabricated polypyrrole and its composites will be discussed. As the concentration of PSS increases from 1 mg/ml to 3 mg/ml, the particle size of polypyrrole would decrease from 50-70 nm to 30-50 nm. All of fabricated polypyrrole are identified to be amorphous feature according to XRD data. From the results of FTIR, Raman, UV-visible and elemental analysis, they show the increasing doping level of polypyrrole as PSS concentration increases. While the concentration of PSS was 2.5 mg/ml, the conductivity of polypyrrole is about 150 S/cm which is higher than any other PSS concentration. For polypyrrole/carbon nanotube composites, the morphology of fabricated composites can be found not only particle-type of polypyrrole but also tube-type of core-shell structure of polypyrrole/carbon nanotube composites which has been further confirmed by TEM image analysis. The results of FTIR, Raman and UV-visible indicate that the increasing doping level of composites as PSS concentration increases. When the concentration of PSS was 5 mg/ml, the composite had the better conductivity about 90 S/cm. The electron numbers for polypyrrole/carbon nanotube composites with 5 mg/ml PSS concentration are determined by the curve of EPR and are consistent with the data of conductivity. For polypyrrole/carbon nanotube composites with various ratios of pyrrole, it was difficult to find bare carbon nanotubes as the ratio of pyrrole increases. At the same time, the conductivity of the composites did not show a clear tendency as the ratio of pyrrole increases. The composite with the better conductivity occurs at PSS: pyrrole weight ratio = 1:2. From the result of TGA analysis, they show the thermal stability of the composites would be also promoted slightly as the ratio of pyrrole decreases. For polypyrrole/carbon nanotube composites with various ratio of carbon nanotubes, the XRD data show traces of diffraction peak at 2θ=26°, corresponding to (002) plane of carbon nanotube. The conductivity of composites did not increase as the content of carbon nanotube increases. Two possible explanations, such as the lower conductivity of CNT and strong doping effect of PSS, can be reached. The electron numbers for polypyrrole/carbon nanotube composites with various CNT ratios decrease as CNT ratio increases. These results are slightly close to those data of conductivity. The thermal stability of composites are enhanced as the content of CNT increases.中文摘要.....I 英文摘要.....III 總目次.....V 圖目次.....VII 表目次.....XI 第一章 緒論.....1 1-1 前言.....1 1-2 研究動機.....3 1-3 研究方向.....4 第二章 文獻回顧.....5 2-1 導電高分子簡介.....5 2-1-1 導電機制.....8 2-2 聚吡咯(polypyrrole, PPy).....11 2-2-1 添加物對聚吡咯的影響.....14 2-3 聚電解質.....22 2-3-1 聚電解質種類.....23 2-4 奈米碳管.....25 2-4-1 奈米碳管之表面改質.....27 2-5 聚吡咯/奈米碳管複合材料.....29 第三章 實驗方法與步驟.....36 3-1 實驗材料.....36 3-2 實驗儀器.....37 3-3 實驗步驟.....38 3-3-1 以PSS作為摻雜劑製備聚吡咯.....38 3-3-2 以PSS製備聚吡咯/奈米碳管(PPy/CNT)複合材料.....40 3-4 實驗儀器分析.....43 第四章 結果與討論.....46 4-1 以PSS摻雜之聚吡咯.....46 4-1-1 以PSS摻雜聚吡咯之形態影響.....46 4-1-2 以PSS摻雜聚吡咯之結構與物性影響.....51 4-2 以不同PSS濃度製備聚吡咯/奈米碳管(PPy/CNT)複合材料.....60 4-2-1 以PSS製備聚吡咯/奈米碳管複合材料之形態影響.....60 4-2-2 以PSS製備聚吡咯/奈米碳管複合材料之結構與物性影響.....65 4-3 改變吡咯單體含量製備聚吡咯/奈米碳管(PPy/CNT)複合材料.....73 4-3-1 吡咯單體含量對聚吡咯/奈米碳管複合材料之形態影響.....73 4-3-2 吡咯單體含量對聚吡咯/奈米碳管複合材料之結構與物性影響.....76 4-4 改變奈米碳管添加量製備聚吡咯/奈米碳管(PPy/CNT)複合材料.....84 4-4-1 奈米碳管添加量對聚吡咯/奈米碳管複合材料之形態影響.....84 4-4-2 奈米碳管添加量對聚吡咯/奈米碳管複合材料之結構與物性影響.....86 第五章 結論.....94 參考文獻.....9