共軛高分子掺合物靜電紡絲纖維之結構形態與光電性質研究

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

曾平(Ping Tzeng)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01571

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。共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。共軛高分子的光電特性，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電特性，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，我們使用兩種共軛高分子(PEDOT:PSS) (P3HT)製備出具有導電性質的靜電紡絲，並使用高分子量的高分子如(PVP) (PMMA) (PEO)等使靜電紡絲的過程更加順利。在噴絲的過程中，我們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，製備出不織布型態的奈米纖維。其次我們也製備出PF-b-PNIPAAm混摻PMMA之靜電紡絲纖維，藉由改變PF-b-PNIPAAm兩部分鏈段的比例，觀察其微相分離的尺度、形態與光物理特性之變化。
本篇論文的第一部分是改變PVP/PEDOT:PSS內外雙軸的流速(0.4-0.8 mL•h-1/0.2-0.5 mL•h-1)，利用雙軸靜電紡絲裝置，成功製備出不織布奈米導電纖維(纖維平均直徑750-1050 nm)。隨著外軸PEDOT:PSS流速的增加，導電纖維的尺寸分布逐漸變大。此外也製備出PMMA不織布靜電紡絲纖維，再將不織布纖維浸泡於導電高分子中以化學吸附的方式使PEDOT:PSS附著於纖維表面上，形成導電纖維。藉由FE-SEM觀察，發現浸泡導電高分子後纖維直徑有些微的增加，而且觀察纖維的表面發現有許多30-90 nm的孔洞產生。兩種導電纖維的導電度都會隨著絕緣部分的高分子含量而改變。PVP/PEDOT:PSS雙軸纖維的導電度隨著內軸PVP濃度的減少可以從2.14E-6 S•cm-1 增加至 4.32E-5 S•cm-1，而PEDOT:PSS/PMMA則是比前者高出三個級數。
第二部分則是將P3HT 導電高分子混摻於PEO，進一步利用靜電紡絲方法搭配特殊的幾何收集器得到奈米導電纖維，我們使用雙軸靜電紡絲裝置，並在外軸部分通入氯仿來減緩內軸的P3HT/PEO(4wt%)高分子溶液在噴嘴快速固化的現象，氯仿還有幫助縮小纖維尺寸製數百奈米的功用，整體來說可以改善電晶體的效能。此外我們也篩選出最佳的材料溶液配方(內軸P3HT50mg•mL-1、外軸PMMA300 mg•mL-1、使用氯苯溶劑、外軸溶液加入10 wt%的TBAP鹽類) ，以及調控操作條件(電壓:17 kV、工作距離:15cm、流速:外軸2mL．h-1、內軸0.1mL．h-1)利用雙軸噴絲的技術達到穩定的cone-jet model，將PMMA部分利用丙酮蝕刻之後成功地製備出純P3HT的導電奈米纖維(纖維直徑約125 nm)。隨著P3HT在導電纖維中的比例增加，元件的mobility也跟著提升，而純P3HT導電纖維製成的元件擁有最高的電洞遷移率0.0034cm2V-1s-1。利用導電纖維製備而成的元件，無論是電洞遷移率、遮蔽電壓、或是開/關電流比例，其性質都無法達到旋轉塗佈薄膜電晶體的程度，主因是纖維的高比表面積使得其迅速被空氣中的水氧摻雜導致效能下降。若元件製備及效能測量都能在真空下操作，相信元件的效果會更佳。
本文的最後一個部分，將團鏈共聚高分子(rod-coil diblock copolymer): PF-b-PNIPAAm與PMMA混摻後，利用雙軸靜電紡絲系統在外軸導入THF溶劑已減緩針頭溶液固化的現象，成功製備出新穎的共軛高分子之靜電紡絲纖維，並利用溫度的改變來探討共聚合高分子在纖維中的形態與光物理性質的變化。首先，從光學顯微鏡和TEM觀察共聚合高分子中PF的形態變化，發現由於含量過少之緣故，並無明顯的尺度或PF團鏈聚集的明顯改變。另外隨著溫度的增加，我們發現PL圖譜會有新的特徵峰出現，而纖維的變化比薄膜更明顯，推測可能的原因是纖維具有較高的比表面積讓共聚合高分子進行形態的改變。此外我們也研究了不同的共聚合高分子軟硬鏈段比對溫度的應答效應變化，結果發現當軟鏈段變長，共聚合高分子會有較強的活動力，因此在PL圖譜上可得到較明顯的變化。將PL圖譜轉換為CIE座標，則得到在低溫(藍色)與高溫(藍紫色)之間有不同的發光光色，未來應可應用於溫度感應器上。
利用靜電紡絲將成功製備成多種型態的導電和發光纖維，藉由調控混摻比例或溫度，進而得到不同導電性質或發光特性的奈米纖維，未來可應用在導電織物、電子元件或是元件感應器上。

關鍵字

靜電紡絲 ； 共軛高分子 ； 結構型態 ； 光電性質

並列摘要

Electrospinning (ES) has emerged as a new technique to produce various functional polymer nanofibers. Conjugated polymers have been extensively studied for various electronic and optoelectronic devices due to the excellent electronic and optoelectronic properties. The electrical and optical 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, conducting electrospun fibers based on poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS) and Poly(3-hexylthiophene-2,5-diyl) (P3HT) were successfully produced. High molecular weight polymers such as poly(vinylpyrrolidone) (PVP), poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) were used to enhance the spinnability. Thermoresponsive poly[2,7-(9,9-dihexylfluorene)]-b-poly[N-isopropylacrylamide] (PF-b-PNIPAAm)/PMMA binary blend fibers were also fabricated. Effects of PF-b-PNIPAAm rod-coil block ratio on the morphology and photophysical properties were studied.
In the first part of this thesis, two conductive electrospun fibers were fabricated. First, conductive PEDOT:PSS(shell)/PVP(core) coaxial electrospun non-woven fibers of the with diameters around 750-1050 nm were successfully prepared from various core/shell flow rates. The diameter distribution became wider as the PEDOT:PSS flow rate enhanced. Conductivity showed an one-order increase from 2.14E-6 to 4.32E-5 S•cm-1 after the core/shell flow rates were tuned. Second, conductive electrospun fibers were fabricated by coating PEDOT:PSS on the surface of PMMA as-spun fibers. Coating cycles were optimized and electrical properties were measured. The conductive fibers showed a slight increase in diameter after coating PEDOT:PSS and porous surface structures with the pore size of 30-90 nm were observed, which were not found on pure PMMA ES fibers. Compare with the PEDOT:PSS/PVP coaxial fibers, a significant enhancement was discovered on the PEDOT:PSS/PMMA fibers with the conductivity as 7.72E-2 S•cm-1. To sum up, the measured conductivity results of the fibers were related to the content of the insulating polymer.
In the second part, conductive electrospun nanofibers with diameters around 230-410 nm were successfully prepared through the P3HT/PEO blends using a single-capillary spinneret and a collector with a rectangular hole-gap. Chloroform was injected into the shell layer to prevent rapid solidification at the nozzle tip and to tune fiber size. The total weight percentage was fixed at 4 wt%, and four composition (1/3, 1.6/2.4, 2/2, 3/1) of the blends were prepared. Pure P3HT nanofibers were also fabricated with average diameter 125nm. The insulating shell PMMA was removed by acetone. The field mobility of the P3HT/PEO blend electrospun fibers increased with enhancing its content from 0.000072 to 0.00017 cm2V-1s-1. The pure P3HT fibers show the highest mobility 0.0034 cm2V-1s-1. All electrical properties including mobility, threshold voltage and on/off ratio were low compare to P3HT thin film FET device due to the high surface-to-volume ratio. The high surface-to-volume ratio causes rapid doping by oxygen and moisture. By operating all the processes in inert or vacuum environment, the performance can be improved in the future.
In the last part, thermoresponsive light emitting electrospun fibers were prepared through the PF-b-PNIPAAm/PMMA blends using a two-fluid spinneret. The shell layer was injected with THF to prevent the rapid solidification occurred at the nozzle tip. The fiber diameter was around 100-1200 nm. Prerequisites for the as-spun fiber formation are developing the cone-jet spinning model. The laser confocal image and TEM results both showed that PF-b-PNIPAAm was well dispersed in the PMMA matrices but difficult to observe PF aggregate domains due to the low content of PF in ES fibers. The PL spectra of the PF-b-PNIPAAm/PMMA blends showed additional shoulders appearing at 470~490 nm as temperature was increased from 20 to 40℃ due to the PF aggregation driven by PNIPAAm moiety. Reversibility was verified by cooling temperature back to 20℃, and the additional shoulder vanished. The color coordinate also exhibited that PF-b-PNIPAAm/PMMA fibers emitting blue light at 20℃ changed to purple blue at 40℃.
The present study demonstrates that various conductive and light-emitting ES nonwoven fibers were successfully produced through optimum polymer composition and device fabrication process, which could have potential applications as conductive fabrics, electronic devices, or sensory materials for smart textiles.

並列關鍵字

Electrospinning ； Conjugated polymer ； Morphology ； Opto-electronic

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