| 摘要: | 本論文主要在電紡織技術中，比較纖維的形成及研究應用，主要重點為(1) 分析連續近場continuous near-field electrospinning (CNFES) 與傳統電紡織技術，(2)以CNFES技術搭配多孔材料產生多根射流，並以理論公式探討射流距離與臨界電場之分布關係，(3)利用乾式轉印技術將Pt纖維轉印至PDMS上，完成具可撓且透明的電極。 (1) 傳統電紡織技術與(CNFES)之分析比較: 本實驗以poly vinylidene fluoride (PVDF)之材料進行傳統電紡織與CNFES技術之薄膜分析比較。實驗的薄膜纖維狀態及纖維平均直徑average fiber diameter (AFD)皆是藉由scanning electron microscopy (SEM)觀察獲得，而Differential scanning calorimetry (DSC)用來比較傳統電紡織與CNFES之結晶率及焓值。且在Fourier Transform Infrared Spectroscopy (FTIR)下可用來尋找PVDF薄膜之同分異構體，結果顯示CNFES薄膜在紅外線下相較於傳統電紡織吸收的震幅較小，此表示CNFES相較於傳統電紡織之纖維有較小的結晶。不過薄膜CNFES相對於傳統電紡織則是有較高的結晶率(40.78%)而傳統電紡織則只為(33.72%)，DSC的結果顯示僅管傳統電紡織與CNFES的纖維尺寸有著明顯差異，但是在熔點及吸熱量則是有極高的相似度。最後觀察傳統電紡織技術中奈米纖維射流之臨界長度，並由實驗結果得到 關係，此實驗的結果也與理論 相符合。(2) CNFES用於自組織多射流: 在本文中，以CNFES技術探討自組織在多根射流下的電場與射流間距關係，並以分散法研究電紡織技術與臨界電場/磁場強度的關係。特別的是，在細微尺度下選擇一個特定的特徵波長，而這波長與理論“形成最快的不穩定”有著重要的關係。本實驗架構是利用兩片銅箔電極夾附著多孔材料，並由polyethylene oxide (PEO)8％之聚合物溶液以CNFES技術由自由液面射出。最後以理論公式推導，並驗證了臨界磁場的強度相對應臨界射流間距的關係，結果顯示即射流相鄰之間的最大距離取決於毛細管長度。然而，除了靜水壓力外，毛細管壓力及電場壓力也都提出擬合理論值，而擬合後的理論值將彌補傳統靜電紡織及CNFES的自由表面力與實驗之差。最後在CNFES下，毛細管外加之壓力在電極與收集板為3-5mm下與理論值有相符。(3) 可排列奈/微米金屬纖維轉印成可撓之透明電極: 銦錫氧化物indium tin oxide（ITO）薄膜材料是製作太陽能電池和顯示器當前主要使用的，但伴隨著需求的增加將使得它的價格越來越昂貴，且ITO脆性的缺點也會讓它即將被取代。最近，以靜電紡織技術製作出長寬比為100,000的銅奈米纖維同時具有 90% 穿透度及50Ω/sq的特性，然而這項技術在製造的同時需伴隨兩項高溫過程，其中分別在空氣中以500◦C的高溫加熱兩小時以及通氫氣以300◦C加熱一小時。本文中，我們將以新製程電紡織纖維模板及乾式轉印技術製作nano/micro金屬線並作為可撓且透明的電極。在這裡，我們將展現我們的高性能透明Pt纖維電極，而我們提出新的製程主要是將以濺鍍與紡織的時間來控制電極的導電率及穿透度optical transmittance (T)，且過程中都無需高溫處理。最後我們得到的Pt纖維電極不但具有5000的長寬比，且經由濺鍍將可降低接觸阻抗。而這結果將讓我們Pt纖維電極得到高T 90%與低的Rs Sheet resistance (Rs) 131 Ω/sq。ITO薄膜的脆性在未來將有可能被具有相當好可撓與拉伸性的透明Pt纖維電極所取代。(1) A comparative study of PVDF nanofibrous membranes prepared by continuous near-field and conventional electrospinning processes:A comparative study utilizing both continuous near-field electrospinning (CNFES) and conventional electrospinning processes of electrospun poly vinylidene fluoride (PVDF)-based membranes (EPMs) is presented in this paper. The fiber morphology and average fiber diameter (AFD) of the EPMs are observed by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) is used to compare the possible modifications in crystal structure and thermal properties. Fourier Transform Infrared Spectroscopy (FTIR) is used to study the crystalline isomers of PVDF EPMs. Results indicate that EPMs prepared by CNFES exhibit slightly lower relative intensities at the infrared absorption bands than the conventional electrospinning counterparts, owing to its smaller size of crystallite. Moreover, the CNFES electrospun fiber are revealed to have relatively higher crystallinity of 40.78%, as compared with conventional ones of 33.72%. However, DSC results indicate that both CNFES and conventional EPMs share similar thermographs in endothermic peaks extending from 156°C to 174°C, despite the significant differences in AFD. Finally, the critical length of PVDF nanofibers is characterized experimentally and theoretical prediction of is in well agreement with the experimental observations of . (2) Self-Organization of multiple jets in Near-Field Electrospinning Process:In this paper, a dispersion law analysis and critical value of applied electric field intensity/field strength formulations are employed to investigate the self-organized behavior of multiple jets in near-field electrospinning (NFES) experiments. In particular, the theoretical “fastest forming instability” in mesocopic scale plays a crucial role in selecting a specific characteristic wavelength. The onset of electrospinning from a free liquid surface is experimentally observed from the porous material sandwiched by 2 flat copper electrodes and NFES setup of electrified 8 wt% polyethylene oxide (PEO) polymeric solution. Predicting critical values of the critical field strength and corresponding critical interjet distance i.e., the maximal distance between the neighboring jets, is also deduced and validated to be simply depends on the capillary length. Subsequently, a modified theory based on the addition of hydrostatic, capillary and electric pressures is proposed to compensate the deviation of NFES experiment and theory of conventional electrospinning from free liquid surface. The extra capillary pressure term is curve-fitted and found to be effective to reduce the deviation in interjet distance range of 3-5mm, which falls into the regime of NFES at the similar scale of electrode-to-collector distance.(3) Pattern transfer of Aligned Metal nano/micro wires as flexible Transparent Electrode using Electrospun Nanofibers template:Owing to scarcity and high cost of indium, predominantly used indium tin oxide (ITO) films as transparent electrodes have attracted great attention in finding potential replacement such as solution-processed networks of carbon nanotubes (CNTs), graphene, and silver nanowires (NWs). More recently, electrospun copper NWs as high-performance electrodes which high aspect ratio of 100,000 and 90% transmittance at 50Ω/sq was experimentally achieved. However, the fabrication route of the Cu nanofibers (NFs) web includes two high temperature processes (calcinated 2h in air at 500◦C and annealed 1h in hydrogen at 300◦C, respectively). In this paper, we proposed a new method in obtaining a metal nano/micro wires as flexible transparent electrode using electrospun NFs templates and dry pattern transfer process. Our proposed method is advantageous in easily tuning the conductivity and transmittance (T) via sputtering time in minutes without the need of time-consuming high temperature thermal steps. Here, we show comprehensively transferred high-performance transparent electrodes with platinum (Pt)-coated NWs electrodes by a facile and scalable electrospinning combined sputtering process. Pt-coated NWs have high aspect ratios of up to 5000 and sputtered with Pt to reduce junction resistance, which result in high T at low sheet resistance, e.g., 90% at 131 Ω/sq. The Pt-coated NWs electrodes also show great flexibility and stretchabilty, which easily surpass the brittleness of ITO films. |
