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  • 學位論文

靜電紡絲製備共軛高分子奈米纖維之形態、光物理性質及應用

Electrospun Conjugated Polymer Nanofibers: Morphology, Photophysical Properties, and Applications

指導教授 : 陳文章

摘要


靜電紡絲是一種能夠將高分子材料製備成多功能性奈米纖維的新穎技術,所以近年來已廣泛地被探討。共軛高分子具有良好之導電及光電效率,可廣泛應用於光電元件上。其共軛高分子的光物理特性,可以藉由高分子混摻亦或是不同的合成方法來調控,以增強在元件應用上的特性,然而,目前的研究多是以共軛高分子薄膜的形態為主,較少探討共軛高分子奈米纖維的形態與光物理特性,主要的原因是對於靜電紡絲製程,共軛高分子有較低分子量與溶劑選擇的限制。因此,本論文的研究目標為設計靜電紡絲製程並操控其製程條件,製備出不同樣式的新穎共軛高分子靜電紡絲纖維(包含不織布、定向性或是核殼纖維的型態),研究其形態與光物理特性,並探討其在感測元件織物上的可能應用,舉凡pH值之酸靈敏感應、偏極光特性、DNA感測、環境檢測。上述的各項特性也與薄膜型態進行比較。 本文的第一個部分(第二章),我們利用單軸靜電紡絲系統,成功製備出以共軛性茀系衍生物之高分子(PFO, PFQ, PFBT, PFTP)混合非共軛高分子(聚甲基丙烯酸甲酯, PMMA)之靜電紡絲纖維。由SEM的結果顯示,PFO/PMMA可發光性之奈米纖維的纖維直徑為250-750nm。而由TEM的測試結果發現,共軛高分子PFO在PFO/PMMA纖維內是以類似纖維狀存在,隨著PFO在整體成份的比例提高,聚集尺度漸增,並且形成一個特殊的核殼結構(core-shell/ PFO-PMMA structure),我們推測這主要是因為相較於PMMA,PFO在氯仿中的溶解度較差,導致其會較快固化於整體纖維的中央。從共軛聚焦顯微鏡的觀察中,我們發現PFO在纖維內的聚集尺度遠小於PFO在薄膜型態的聚集尺度,故相較於薄膜,經由静電紡絲製程能夠降低共軛高分子的聚集,使得發光顏色較為藍移,並且有較高的發光量子效率。藉由混合入不同的茀-受體交替共聚高分子於PMMA中,我們可以製備出不同發光的奈米纖維,獨特的發光奈米纖維如PFO/PMMA, PFQ/PMMA, PFBT/PMMA, PFTP/PMMA,其最大放光波長/顏色分別如下: (443nm/藍色)、(483nm/綠色)、(539nm/黃色)、(628nm/紅色)。此部分的研究證實,我們利用共軛性茀系衍生物之高分子混合非共軛高分子,以靜電紡絲技術製備而得的靜電紡絲纖維,可以得到全光色之特殊的發光奈米纖維。 本文的第二個部份(第三章),我們利用單軸靜電紡絲系統再搭配自製的收集器,將共軛性茀系衍生物之高分子(PFO與PF+)分別與非共軛性高分子(聚甲基丙烯酸甲酯, PMMA)混合後,製備出具備高度定向的共軛高分子混合之靜電紡絲纖維。利用SEM觀察可發現不同收集器的中空寬度會影響纖維的定向程度,其中以寬度在0.5-1.5公分者為最佳,且其纖維具備高度定向性,而纖維直徑細度是250-500nm,纖維表面平滑不具備孔洞。利用TEM觀察出PFO的微相分離形態在纖維裡頭是平行整根纖維,而PF+則是呈現週期性的延纖維方向進行聚集。相較於不織布或是薄膜形式,這樣子的定向性纖維具備高達4倍的偏極光效果。除此之外,在PF+與PMMA混合的奈米纖維,由於比薄膜具備較高的比表面積,因此能夠有更靈敏的DNA質體感測效果。因此,此章節所研究製備的定向性纖維具備有偏極光以及感測質體DNA的特性,在光電元件與感測應用上具備潛力。 本文的第三個部份(第四章),分別將兩種團鏈共聚合高分子(rod-coil diblock copolymer): PF-b-PMMA或是PPQ-b-PS,利用單軸靜電紡絲系統,成功製備出新穎的共軛高分子之靜電紡絲纖維,並利用溶劑選擇效應,探討共聚合物高分子在纖維中的形態與光物理性質特性的不同。首先,我們將PF-b-PMMA共聚合物高分子,分別從三種不同THF/DMF混合的溶劑系統中製備成奈米纖維,從實驗的結果中發現,不同的溶劑系統會使得在纖維內的PF團鏈聚集的形態與尺度發生轉變,在THF中會形成尺度在5-10nm的點狀(dot-like),於THF/DMF (50/50)則是以尺度在10-20nm的線狀(line-like)存在,而在DMF中則是尺度在25-50nm的橢圓形狀(ellipse-like),隨著DMF在混合溶劑系統中的比例增加,不但使得纖維的直徑細度降低,並且由於DMF是PF團鏈的不佳溶劑(poor solvent),因此造成PF團鏈的聚集尺度增加,進而使得UV-vis吸收波長與光激發光波長(absorption or luminescence spectra)產生紅移的現象(red-shifting)。從我們的研究中証實,我們能夠成功製備出PF-b-PMMA放射藍光的奈米纖維,並經由溶劑選擇效應,藉由PF團鏈聚集形態與尺度的改變進而調控光色的變化。其次,我們亦將PPQ-b-PS共聚合物高分子,分別溶在三種不同的溶劑系統(dichloromethane, chlorobenzene, and chloroform)後,利用單軸靜電紡絲系統將其製備成奈米纖維,發現不同的溶劑會使得PPQ-b-PS產生不同程度的聚集,進而有不同的發光光色(綠、黃、橙色)。除此之外,更深入探討硬桿-柔軟嵌段共聚高分子的靜電紡絲纖維用於pH 感應器方面的應用。結果顯示不同溶劑製備的纖維,其對酸的感應程度隨著硬桿端高分子的聚集程度上升而下降。而由靜電紡絲製備的纖維會比其固態薄膜的感測性高。 本文的第四個部分(第五章),我們利用雙軸的系統,製備出具有感測環境能力的核(PMMA)殼(P3HT)雙成分奈米纖維。這樣子的核(PMMA)殼(P3HT)雙成分奈米纖維,經由SEM觀察發現其纖維的直徑為500-700nm,且其纖維的表面均勻覆蓋著類似P3HT的特徵形態(worm-like)。當纖維放置在室溫大氣可見光的環境之下,隨著時間的增加,纖維的發光顏色會從紅光轉變到橘光,到兩週後呈現綠光的顏色,這主要是由於發生高分子鏈段的降解,導致共軛長度減短所致。除此之外,由於P3HT/O2的複合物形成(charge transfer complex, CTC),使得兩週後的纖維在沒有進行doping下,發現具有導電的特性。然而,以上特殊的光電現象,則在薄膜的形態並沒有明顯地發現,故我們製備出的核(PMMA)殼(P3HT)雙成分奈米纖維是具備環境感測能力的潛力。

並列摘要


Electrospinning (ES) has emerged as a new technique to produce various functional polymer nanofibers. Conjugated polymers have extensively studied for diverse electronic and optoelectronic devices due to the excellent electronic and optoelectronic properties. The photophysical properties of conjugated polymers could be tuned through the approaches of blending or different synthetic ways which result in the enhancement of device characteristics. However, most of the above studies are based on the thin film devices. The morphology and properties of conjugated polymers based ES nanofibers have not been fully explored yet. Only few ES nanofibers based on conjugated polymers were reported because of the limitation on molecular weight or solvents. In this thesis, the objectives are to produce diverse ES nanofibers (nonwoven, aligned, or core-shell type) based on various conjugated polymers and explore their morphology, photophysical properties, and applications, including distinguishing polarized characteristic and sensory devices and further those exhibited significant difference in comparison to the thin films. In the first part of this thesis, Light-emitting electrospun (ES) nanofibers were successfully prepared through the binary blends of polyfluorene derivative/poly(methyl methacrylate)(PMMA) using a single-capillary spinneret. The studied poly(fluorene)s included poly(9,9-dioctylfluoreny-2,7-diyl)(PFO), poly [2,7-(9,9-dihexylfluorene)-alt-5,8-quinoxaline](PFQ), poly[2,7-(9,9-dihexyl-fluorene) -alt-4,7-(2,1,3-benzothiadiazole)](PFBT), and poly[2,7-(9,9-dihexyl-fluorene)-alt -5,7-(thieno[3,4-b]pyrazine)](PFTP). The TEM and SEM results suggested that PFO/PMMA ES fibers gradually formed a core-shell structure with a porous surface as the PFO blend ratio was increased. PFO has a poorer solubility in chloroform than PMMA and forced it to be solidified first in the fiber center to form the core-shell structure. The SEM and laser confocal images suggested that the PFO aggregation domain in the ES fibers was much smaller than that in the spin-coated films and resulted in higher photoluminescence efficiency. Uniform ES fibers produced from the binary blends of PFO/PMMA, PFQ/PMMA, PFBT/PMMA, and PFTP/PMMA exhibited the luminescence characteristics (peak maximum(nm); color) of (443; blue), (483; green), (539; yellow), and (628; red), respectively. The present study demonstrates that full color light-emitting ES nanofibers could be produced from the binary blends of polyfluorene derivative/PMMA. In the second part of this thesis, highly aligned luminescent electrospun (ES) nanofibers were successfully prepared from two binary blends of poly(9,9-dioctylfluoreny-2,7-diyl)(PFO)/ poly(methyl methacrylate)(PMMA) and poly(9,9-di(3,3-N,N-trimethyl-ammonium)-propylfluorenyl-2,7-diyl)-alt-(9,9-dioctylfluorenyl-2,7-diyl)diiodide salt (PF+)/ PMMA. The PFO/PMMA aligned ES fibers showed a core-shell structure but the PF+/PMMA exhibited periodic aggregate domains in the fibers. The aligned fibers had polarized steady-state luminescence with a polarized ratio as high as 4, much higher than the nonwoven ES fibers or spin-coated film. Besides, the PF+/PMMA aligned ES fibers showed an enhanced sensitivity on sensing plasmid DNA. Such aligned ES fibers could have potential applications in optoelectronic or sensory devices. In the third part of this thesis, Novel luminescent electrospun (ES) fibers were successfully prepared from a conjugated rod-coil block copolymer, poly[2,7-(9,9-dihexylfluorene)]-block-poly (methylmethacrylate) (PF-b-PMMA) using a single-capillary spinneret. The experiment results indicated that PF-b-PMMA ES fibers prepared from THF, THF/DMF (50/50) and DMF contained PF block aggregated structures of dot-link (5-10 nm), line-like (10-20 nm), and ellipse-like structure (25-50 nm), respectively. Such variation on the aggregation size led to the red-shifting on the absorption or luminescence spectra. Also, the fiber diameters decreased with enhancing the DMF content. Furthermore, functional ES fibers with a high sensitivity on acid or pH were successfully prepared from binary blends of poly(phenylquinoline)-block-polystyrene rod-coil diblock copolymers (PPQ-b-PS) /polystyrene (PS). The effect of pH on the fluorescence spectra for ES fibers and spin-coated thin film were investigated. The PPQ-b-PS /PS ES fibers showed high sensitivity in comparison with the spin-coated film. The present study demonstrates that blue light-emitting ES fibers were successfully prepared from conjugated rod-coil diblock copolymer and their aggregate morphology and photophysical properties could be tuned through selective solvent. Furthermore, it also suggested that the ES fibers prepared from rod-coil conjugated block copolymer could have potential applications in optoelectronic or sensory devices. In the fourth part of this thesis, new electrospun (ES) sensory fibers consisted of poly(methyl methacrylate) (PMMA) core and poly(3-hexylthiophene-2,5-diyl) (P3HT) shell were successfully prepared using a two-fluid coaxial electrospinning process. The studies showed that the prepared ES fibers had diameters of 500-700 nm and worm-like surface structure of P3HT on the fiber. Upon exposed to air under visible light for two weeks, significant blue-shifting on both absorption and luminescence spectra (from red, to orange, and to green PL emission). It was probably due to the chain scission occurred in the P3HT and led to the reduced conjugated length. The sensitivity of the ES fibers was much better than that of the spin-coated P3HT film from the comparison on the variation of photophysical properties. Besides, the EPR measurements suggested the formation of the P3HT.O2 charge transfer complex (CTC), leading to the fiber conductivity without an external doping. The present study demonstrates that conjugated polymer based ES core-shell fibers may have potential applications for oxygen-sensing devices.

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