靜電紡絲高分子掺合物之形態分析及其於場效應電晶體以及氣體感測應用研究

Abstract

靜電紡絲是一項獨特且廣為應用於各領域的技術，此技術的最大特點在於可以製備奈米等級的纖維，相較於傳統製備方式，可以把纖維從微米尺度提升至奈米尺度，進而大幅度提高纖維的比表面積。此外，在施加高電壓後，靜電紡絲在溶液鞭甩的過程中，具備強烈的幾何限制效應與電場影響，可以使纖維形成某種特定排列。故本論文的研究目標致力於靜電紡絲應用在感測系統以及場效應電晶體的效能影響。 1.側鏈結晶性對於混摻聚(3-己烷基噻吩)與聚(丙烯酸酯類)雙軸靜電紡絲在場效應電晶體的應用與型態分析(第二章) 本研究探討聚(丙烯酸十八酯)與聚(丙烯酸十二酯)的側鏈作用力對於聚(3-己烷基噻吩)載子移動率的影響以及靜電紡絲的纖維型態。純聚(3-己烷基噻吩)纖維的載子移動率為 1.92 × 10-4 cm2 V-1 s-1，然而在混摻聚(丙烯酸十八酯)後，其載子移動率可大幅度增加約兩個數量級，在P3HT/PSA(1:0.2)比例有最佳值3.21 × 10-2，由差式熱量掃描儀分析，P3HT的融解熱為10.32、15.24、13.8以及 13.96分別在P3HT/PSA混摻比例是1:0 1、1:0.2、1:0.5和1:1。此明顯差異可以歸功於在電紡過程中，P3HT與PSA形成相分離，P3HT先結晶後外圍具結晶性的PSA再結晶，因為P3HT的主鏈和側鏈與PSA作用力不同，P3HT主鏈與PSA相容性較差，所以PSA可以誘導P3HT的主鏈排列更緊密。然而，當混摻較低結晶性的PnLA時，PnLA與P3HT的主鏈和側鏈的作用力差不多，誘導效果並不明顯，所以P3HT結晶提升程度較混摻PSA來的低，導致較低的載子移動率，但是仍具備提升的效果。然而在旋轉塗佈成膜的製程之下，PSA仍具備有提升P3HT載子移動率的效果，但是在靜電紡絲的製程中，高分子鏈會受到強烈的拉伸以及幾何形狀限制，可以進一步誘導P3HT的排列，因而得到比旋轉塗佈成膜製程較高的P3HT結晶程度和較高的載子移動率。此外，混摻低比例的PSA對於結晶方向性排列沒有太大影響，但是在高比例時，太多的聚(丙烯酸酯類)導致導電程度變差以及增加相分離的難度，而使的P3HT排列較困難變成無方向性。再者，經靜電紡絲後，纖維內部是P3HT傾向在內層而PSA喜好在外層，因此PSA的緻密結晶層可以有效地阻擋水氣以及氧氣的侵蝕，而在大氣下表現良好的電晶體穩定性。 2.靜電紡絲應用於嵌段式共聚物(N3-PNIPAAm-b-PNMA)包埋DAQ在感測一氧化氮的製備與應用(第三章) 感測分子DAQ成功包埋在PNIPAAm-b-PNMA，並成功經由靜電紡絲技術製備出奈米纖維膜，用以感測一氧化氮氣體。感應原理為DAQ 上兩個鄰位的氨基與一氧化氮反應，形成一個三氮五元環的結構，使得DAQ在520 nm的吸收峰消失。相較於一般薄膜，奈米纖維膜擁有極大的比表面積，可以增加水的通透性，整體反應時間最多可以從90分鐘降低到40分鐘，相當於提高反應速度兩倍的程度。再者，高分子基材包含了具溫感性質的PNIPAAm以及可自我化學交連的NMA鏈段，不同嵌段的高分子對於型態和感測能力影響如下。PNIPAAm為一具有LCST的溫感性材料，其對溫度敏感的膨脹收縮性質，會讓高分子基材隨溫度呈現疏水或親水狀態，進而讓感測系統具備開/關的特色；PNMA為化學交連的鏈段，經過熱交連後會從親水性變成疏水性，使基材在水中仍維持纖維型態，越長的PNMA鏈段在水中維持越明顯的輪廓但是降低纖維的透水能力，進而減少感測敏感度。

Electrospinning technique is a promising method in preparing nanofibers owing to its notable features such as low cost in fabrication, accessible adjustment in morphology, and continuously high-throughput production. In general, electrospun (ES) nanofibers are with high aspect ratio, which is beneficial for sensory or transistor device applications. However, the morphology as well as the application of the polymer-blend-based electrospun nanofibers has not been fully explored yet. Therefore, in this thesis, the influence of the morphology of the polymer-blend-based electrospun nanofibers on the performance of the organic field transistors (OFETs) and the gas sensory devices was investigated and the details were demonstrated as follows. In Chapter 2, side-chains crystallinity effect on Morphology and nanofiber Field-Effect Transistor Characteristics of Crystalline Poly(3-hexlthiophene) and Poly acrylates Blends. We reported the morphology and nanofiber field-effect transistor characteristics based on crystalline poly(3-hexylthiophene)(P3HT) and poly(stearyl acrylates)(PSA) blends in different fabricated processes. P3HT/PSA nanofiber-based field effect transistor was fabricated via coaxial electrospinning technique. The average field effect mobility of the P3HT/PSA blend nanofibers was enhanced to be 3.21 × 10-2 cm2 V-1 s-1 while the blending ratio was equal to 1:0.2, which was two orders of magnitude higher than that (1.92 × 10-4 cm2 V-1 s-1) of P3HT. In addition, enhancing hole mobility of 1.22 × 10-2, 1.17 × 10-2 and 1.6 × 10-3 cm2 V-1 s-1 were also observed when the P3HT/PSA blend ratios were 1:0.5, 1:0.7 and 1:1, respectively. From the DSC analysis, the endothermic heats of P3HT were 10.32, 15.24, 13.83, and 13.96 J/g with different P3HT/PSA blending ratio of 1:0, 1:0.2, 1:0.5 and 1:1, respectively, which suggests that P3HT forms a more compact structure in the prepared nanofibers after blending with PSA. It might be attributed to that the compatibility between the P3HT hexyl chains and PSA probably enhances the molecular stacking within the thiophene rings of P3HT. Besides, the field-effect transistor based on spin-coated film also exhibited the similar effect, but the improving crystallinity effect is worse than ES process. Since the ES strong stretching force and the geometrical confinement associated with the ES process could induce the orientation of polymer chains along the long axis of fiber. As evidenced by TEM and XRD, the morphology studies showed that P3HT/PSA formed a core-sheath structure, which prevents the penetration of moisture and oxygen and results in an enhancement in the air stability of the P3HT. It was also found that at low PSA content, both face-on conformation and edge-on packing of P3HT molecules were coexisted. However, P3HT became randomly orientated as the amount of PSA was raised. In Chapter 3, the NO gas sensing application of ES nanofibers prepared from thermo-responsive poly (NIPAAm-b-NMA)/1,2-diaminoanthraquinone (DAQ) blend was explored. The electrospun (ES) nanofibers of PNIPAAm-b-PNMA were prepared using a single-capillary spinneret and successfully embedded with 1,2-diaminoantraquinone (DAQ) to fabricate gas sensory devices. The high surface/volume ratio of the ES nanofibers efficiently enhanced the responsive speed compared to the drop-cast film, which reduced the reaction time from 90 min to 40 min. Moreover, the polymer matrix comprised of thermal responsive moiety of PNIPAAm and chemical cross-linking moiety of PNMA. The effects of the copolymer compositions on the morphology and properties of the prepared ES fibers were explored. The prepared nanofibers with DAQ revealed outstanding wettability and dimension stability in the aqueous solution. The sensing ability of the prepared nanofibers on the NO gas showed on/off characteristic as the temperatures varied from room temperature to 45 0C due to the LCST characteristic of PNIPAAm at 32 0C.