Morphology and Photophysical Properties of Electrospun Nanofibers Prepared from Conjugated Polymer Blends

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。軛高分子具有良好之導電及光電效率，被廣泛應用於光電元件上。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，但是，目前的研究多是以共軛高分子薄膜的型態為主，較少探討共軛高分子奈米纖維的形態與光物理特性，主要原因是其分子量以及溶劑的限制，故極少文獻將共軛高分子經由靜電紡絲製備成奈米纖維。在本論文中，我們將兩種共軛高分子(PFO/ DB-PPV)混摻非共軛高分子(PMMA)，篩選最佳的材料溶液配方，並調控靜電紡絲的製程參數與收集器，製備出不織布或定向性型態的奈米纖維，其次，藉由改變PFO/ DB-PPV的比例，觀察其微相分離的尺度、形態與光物理特性之變化。篇論文的第一部分是將不同比例的PFO/ DB-PPV(0/10~10/0)發光高分子(10 wt%)混摻於PMMA，利用一般的靜電紡絲方法，成功製備出不織布奈米發光纖維(纖維平均直徑400~700 nm)，由於使用具高揮發度的氯仿溶劑，藉由FE-SEM觀察，發現纖維表面具有許多10-50 nm的孔洞，而經由TEM觀察PFO與DB-PPV微相分離的形態與尺度，發現DB-PPV是以球狀(1-60 nm)聚集於纖維中，而PFO則是以類似纖維狀(20-40nm)存在，若將DB-PPV比例降低(PFO相對比例提高)，DB-PPV球形尺度會下降，PFO則會由不連續的纖維形成連續性的纖維。因此，藉由調控PFO/DB-PPV比例(0/10~5/5~10/0)，改變兩者的微相分離形態與尺度，控制PFO能量轉移給DB-PPV的效能，我們可以得到一連串由藍光(波長426 nm) 藍綠光、到綠光(波長523 nm) 的發光顏色，並且當PFO/DB-PPV/PMMA比例為9.9/0.1/90時，可製備出最高量子效率達80%之發光奈米纖維。二部分則是將不同比例的PFO/DB-PPV(0/10~10/0) 發光高分子(10 wt%)混摻於PMMA，進一步利用靜電紡絲方法搭配特殊的幾何收集器，我們篩選出最佳的材料溶液配方(總濃度為250 mg/ml、使用氯苯溶劑、加入4 wt%的TBAP鹽類)，以及調控操作條件(電壓:5-10 kV、工作距離:15 cm、流速:1 ml/hr)，以達到穩定的Cone-jet model，因而成功地製備出具備高度定向性且兼具偏極光特性的奈米發光纖維(纖維直徑600~800 nm)。由於此部份使用較高沸點的氯苯溶劑，藉由FE-SEM觀察，發現纖維表面平滑且無孔洞產生。偏極化的螢光光譜儀，能夠偵測纖維內規整及具方向性的分子結構，故當共軛高分子鏈段平行或垂直於定向性纖維時，就能產生偏極化的螢光特性。不同於DB-PPV在纖維中是以球狀(1~60 nm)散亂分布，PFO則是以類纖維狀(20~40 nm)平行於整條定向性的纖維方向中，因此，PFO/DB-PPV(10/0)的偏極光倍率(2倍)比PFO/DB-PPV比例(0/10)的偏極光倍率(1.5倍)為高。故我們利用PFO比DB-PPV有較高的偏極光特性，當改變不同偏極板的角度，能夠使PFO/DB-PPV/PMMA(9/1/90)的定向性奈米纖維表現出不同的發光顏色。用靜電紡絲將PFO/DB-PPV/PMMA成功製備成不織布或定向性發光纖維，藉由調控不同PFO與DB-PPV混摻比例，改變兩者的微相分離形態，可以得到ㄧ不同發光顏色以及兼具偏極光發光特性的奈米纖維，未來可應用在智慧型紡織品或是元件感應器上。Electrospinning (ES) has emerged as a new technique to produce various functional polymer nanofibers. Conjugated polymers have extensively studied for various 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 thin film devices. The morphology and properties of conjugated polymers based nanofibers have not been fully explored yet. Only few ES nanofibers based on conjugated polymers were reported because of the limitations on molecular weight or solvents. In this study, luminescence electrospun poly(9,9-dioctylfluorenyl -2,7-diyl) (PFO)/2,3-dibutoxy-1,4-poly(phenylene vinylene) (DB-PPV)/poly(methyl methacrylate) PMMA ternary blend nanofibers were successfully produced. Effects of PFO/DB-PPV ratio on the morphology and photophysical properties were studied, where the PMMA weight percentage was fixed at 90 wt%.n the first part of this thesis, luminescent electrospun PFO/DB-PPV/PMMA ternary blend non-woven nanofibers were successfully prepared from different blending ratios of PFO/DB-PPV/PMMA (0/10/90-10/0/90). The field-emission scanning electron microscope (FE-SEM) studies showed that obtained fibers had the diameters around 400-700 nm and pore size in the range of 10-50 nm. The porous surface structure is resulted from the rapid evaporation of the high volatile chloroform solvent during the ES process. Transmission electron microscopy (TEM) studies showed morphology and size of PFO/DB-PPV micro phase separation in fibers, it was discovered that DB-PPV aggregated as spheres (1-60 nm) in the fibers, while PFO formed fiber-like structures (20-40 nm). The emission colors of the PFO/DB-PPV/ PMMA blend ES fibers changed from green, aquamarine blue, to blue, as the PFO composition increased. Our results showed that various light-emitting color ES fibers were produced through optimum polymer composition and Förster energy transfer. In additions, the high-light-emitting emission fibers obtained from the PFO/DB-PPV/ PMMA blend ratio of 9.9/0.1/90 had an excellent fluorescence quantum yield of 80%. In the second part of this thesis, highly aligned luminescent electrospun nanofibers were successfully prepared through PFO/DB-PPV/PMMA blends by using a single-capillary spinneret and a collector with a rectangular hole-gap. Uniform and aligned PFO/DB-PPV/PMMA blend fibers with diameters ranging from 600-800 nm were observed by FE-SEM. In addition, non-porous and smooth surface is exhibited in such blend aligned ES fibers since high boiling point chlorobenzene solvent is used during the ES process. Besides, a PFO/DB-PPV (10/0) system had a much higher dichroic ratio of 2 than a PFO/DB-PPV (0/10) system, whose dichroic ratio was 1.5. According to the above study, we took the advantage that PFO had a higher polarized emission than DB-PPV to perform different emission colors in PFO/DB-PPV/PMMA (9/1/90) blend system by tuning the angle of polarizer. The present study demonstrates that various light-emitting and polarized steady-state luminescence ES PFO/DB-PPV/PMMA ternary blend nanofibers were successfully produced, which could have potential applications as new light sources, sensory materials for smart textiles, or optoelectronic devices.論文口試委員審定書.....................................................................................................i誌................................................................................................................................iibstract........................................................................................................................ iii文摘要.................... ivontants......................................................................................................................viiable Captions ixigure Captions xhapter 1 Introduction 1-1 Introduction to Electrospinning 1 1-1-1 Development of Electrospinning 1-2 Process Design for Aligned Fibers 3-3 Light-Emitting Electrospun Nanofibers : Morphology and Photophysical Properties 6-4 Photophysical properties of conjugated polymer blends 7-5 Research Objectives 8hapter 2 Experimental Section 20-1 Materials 20-2 Characterization 21-3 Conditions of Experimental Analysis 21-4 Calculation 23hapter 3 Morphology and Photophysical Properties of Various Colors Light-Emitting Electrospun Nonwoven Nanofibers Prepared from PFO/DB-PPV/PMMA Ternary Blends 29-1 Introduction 29-2 Experimental 30-3 Morphological Properties of Electrospun Fibers 31-4 Photophysical Properties of Electrospun Fibers 34-5 Conclusions 36hapter 4 Highly Aligned light-emitting Electrospun Nanofibers Prepared From PFO/DB-PPV/PMMA Ternary Blends: Fabrication, Morphology and Photophysical Properties 52-1 Introduction 52-2 Experimental 53-3 Fabrication and Morphology of Aligned PFO/DB-PPV/PMMA Electrospun Nanofibers 54-4 Photophysical Properties of Aligned and Nonwoven Fibers 56-5 Polarized Luminescence Properties 57-6 Conclusions 60hapter 5 Conclusions 74eferences…. 7