刺激應答靜電紡絲奈米纖維之製備、結構分析及感測應用

Abstract

靜電紡絲技術因其具備了便宜、易使用，且可簡單地將可控制的高分子結構製備成奈米尺度的纖維，所以近年來已廣泛地被研究討論。多功能性刺激應答型靜電紡絲奈米纖維，可藉由與曝露在外在的氣體、酸鹼值、溫度以及金屬離子等反應，來改變一個或多種的特性，如表面型態、光致發光及潤濕性等。然而大部份先前的文獻還是以溶液及薄膜的形態為主，而非奈米纖維。具備著高比表面積優點的靜電紡絲奈米纖維對於不一樣的刺激應答皆可達到高的感測靈敏性。在本論文中，我們設計且製備出多種不一樣結構的多功能性共聚物且將其製備成靜電紡絲奈米纖維，並探討其在多種感測元件上的應用，其結果詳述如下。 在本文的第一部份(第二章)，我們成功製備出由DAQ混摻P(NIPAAm-co-NMA)高分子之靜電紡絲奈米纖維。實驗結果顯示出此具非孔洞性且整齊的P(NIAAm:NMA)(100:20)/1.5wt% DAQ靜電紡絲奈米纖維具有最快的感測NO(g) 特性。原因為高分子中最佳化比例的NMA可以有效的維持住纖維在水中的表面型態。另一方面，因為NIPAAm基團具有低臨界流體溫度的特性，當溫度介於25至50℃時，可以發現其感測NO(g)時的吸收光譜會有明顯的”開/關”交換現象。 本文的第二個部份(第三章)，我們經由自由基聚合反應以及靜電紡絲技術製備出不規則共聚物poly(HPBO-co-NIPAAm-co-SA)多功能性靜電紡絲奈米纖維。 HPBO、NIPAAm和SA部份分別是設計成用來當作鋅離子(Zn2+)和酸鹼的感測、溫度感測以及物理交聯化合物。而由此共聚物(組成比例為HPBO:NIPAAm:SA = 1:93:6)所製備出的靜電紡絲奈米纖維展現出對於鋅離子的卓越偵測靈敏性(濃度可低至10-8 M)。因為在與鋅離子感測鍵結之後其經由光致發光產生的最大發散波長會有75 nm的藍位移發生，且其發光強度也增加了2.5倍。此外，此奈米纖維也展現出在10 °C與 40 °C的溫度循環變化中大量的體積(或是親-疏水性)變化。將這個奈米纖維置於感測鋅離子或鹼性的條件下時，我們發現隨著不一樣的溫度變化將會有個明顯的”開-關”光致發光現象產生。 本文的第三個部份(第四章)，我們利用單軸靜電紡絲技術成功的製備出不規則共聚物poly(FBPY-co-NIPAAm-co-SA)螢光靜電紡絲奈米纖維。由共聚物(NIPAAm:SA:FBPY = 1:93:6)所製備出的平滑奈米纖維因具有較高的比表面積，所以對於鋅離子的感測擁有較佳的靈敏性(最低可至10-5M)，而相同高分子所製成的薄膜其感測靈敏性則只有10-3M。為了更進一步提升感測上的表現，我們也另外製備出了多孔洞性的奈米纖維並且於針對鋅離子的感測上得到了比三種狀態中更好的靈敏性-10-6 M (高分子於THF溶液中的靈敏度約為10-5 M)。另外當溫度由40℃降低至10℃時，由於 NIPAAm基團疏水與親水間的特性轉換，這些奈米纖維也展示了有趣的”開/關”行為。 本文的第四個部分(第五章)，我們成功經由靜電紡絲技術把不規則共聚高分子poly(BPYP-co-NIPAAm-co-SA)製備出新穎性且具光滑和多孔洞性的纖維。由高分子 (BPYP:NIPAAm:SA = 1:93:6)所製備出的多孔性奈米纖維因具有較高的比表面積，所以對於鋅離子的感測擁有優越的表現(濃度最低可至10-8M)，而相同高分子所製成的薄膜與平滑性的奈米纖維其感測靈敏性為10-6M與10-7M。而因鎘離子對於BPYP感測基團的形成常數比鋅離子高，多孔性奈米纖維在感測鎘離子時展現出最佳的靈敏性表現為10-10M。另外當溫度由40℃ 降低至10 ℃時，這些奈米纖維在螢光光譜中也同樣展示出了有趣的”開/關”行為。 綜上所述，可發現這些具有高比表面積的靜電紡絲奈米纖維與其薄膜態比較起來偵測靈敏性皆有明顯的提升，顯示出其在於超高感測元件的應用上深具潛力。

Electrospinning technique has been extensively studied because it is inexpensive, facile, and enables nanometer-scaled fibers with controllable structures. Multifunctional stimulus-responsive electrospun (ES) nanofibers could change one or more properties, such as morphology, photoluminescence and wettability upon exposure to external signals such as gas, pH, temperature or metal ions. However, most aforementioned studies were based on solutions or thin films, but not on nanofibers. ES nanofibers with the advantage of high surface-to-volume ratio could achieve high sensitivity toward different stimuli. In this thesis, we design and prepare ES nanofibers with different structures using multifunctional copolymers for various sensory applications, as described in the following. In the first part of this thesis (Chapter 2), multifunctional ES nanofibers were successfully prepared from the poly((N-isopropylacrylamide)-co-(N-hydroxymethyl acrylamide)) (poly(NIPAAm-co-NMA)) blending with 1,2-diaminoanthraquinone (DAQ). The experimental results show that non-porous and uniform P(NIPAAm:NMA) (100:20)/1.5wt% DAQ ES nanofibers exhibit the fastest NO(g) sensing characteristic due to the optimized NMA content for maintaining the fiber morphology in water. On the other hand, a significant on/off switching of the UV-vis absorption spectra on detecting the NO(g) were observed during 25 and 50℃ due to the low critical solution temperature (LCST) characteristic of the NIPAAm moiety. In the second part (Chapter 3), multifunctional ES nanofibers were prepared from random copolymers of poly{2-{2-hydroxyl-4-[5-(acryloxy)hexyloxy]phenyl} benzoxazole}-co-(N-isopropylacrylamide)-co-(stearyl acrylate)} (poly(HPBO-co- NIPAAm-co-SA)) using free-radical polymerization and followed by electrospinning. The moieties of HPBO, NIPAAm, and SA were designed to exhibit zinc ion (Zn2+) and pH sensing, thermoresponsiveness, and physical cross-linking, respectively. The ES nanofibers prepared from the copolymer (1:93:6 composition ratio for HPBO/NIPAAm/SA), showed ultrasensitivity to Zn2+ (as low as 10-8 M) because its photoluminescence emission maximum underwent a blue shift of 75 nm, and the emission intensity was enhanced 2.5-fold after detecting Zn2+ ion. Furthermore, the nanofibers exhibited a substantial volume (or hydrophilic–hydrophobic) change during the heating and cooling cycle between 10 °C and 40 °C. Such a temperature-dependent variation of the prepared nanofibers under a Zn2+ or basic condition led to a distinct on–off switching of photoluminescence. In the third part (Chapter 4), fluorescent ES nanofibers prepared from random copolymers of poly{[9,9-dihexylfluorene-2-bipyridine-7-(4-vinylphenyl)]-co- (N-isopropylacrylamide)-co-(stearylacid)} (poly(FBPY-co-NIPAAm-co-SA) were successfully prepared from the electrospinning technique with a single-capillary spinneret. The smooth nanofibers prepared from the copolymer (FBPY:NIPAAm:SA = 1:93:6) demonstrated superior sensitivity as low as 10-5 M in sensing zinc ions as compared to polymer films (10-3 M) due to the high specific surface area of nanofibers. The porous nanofibers were also manufactured to further enhance sensing performance and got the best sensitivity (10-6 M) among three states when sensing with zinc ions (sensitivity of polymer solution in THF was about 10-5 M). These nanofibers also exhibited an interesting “on/off” switch behavior with decreasing temperature from 40 to 10 ℃ due to the hydrophobic-hydrophilic transition of NIPAAm moiety. In the fourth part (Chapter 5), multifunctional electrospun porous fibers prepared from random copolymers of poly{2-{6-[5-(pyrene-3-yl)pyridine-2-yl] pyridine-3-yl-amino} ethylacrylate-co-(N-isopropylacrylamide)-co-(stearylacrylate)]} (poly(BPYP-co-NIPAAm-co-SA) were successfully prepared from the electrospinning technique with a single-capillary spinneret. The polymer porous fibers prepared from 1:93:6 composition ratios for BPYP/NIPAAm/SA showed a superior performance (10-8 M) in sensing zinc ions as compared to polymer films (10-6 M) and smooth fibers (10-7 M) due to the higher specific surface area than those of films and smooth fibers. Cadmium ion, with the higher formation constant than zinc ion with the BPYP probe, showed the best performance in 10-10 M by porous fibers. These fibers also exhibit an off/on switch behavior as the temperature decreased from 40 to 10 oC due to the hydrophobic-hydrophilic transition of NIPAAm moieties which cause the gradual swelling of fibers. The high surface-to-volume ratio of the above ES nanofibers significantly enhanced their sensitivity compared to that of thin films, which have the potentials in ultrahigh sensory device applications.