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標題: | 電紡高分子噴流之三維不穩定性分析 Three Dimensional Instability of Polymer Jet in Electrospinning |
作者: | Tang-Hsuan Huang 黃塘軒 |
指導教授: | 陳發林(Fa-lin Chen) |
關鍵字: | 電紡,奈米絲,高分子,黏彈性流體,穩定性分析,電流體力學, Electrospinning,Nanofibers,Polymer,Vicoelastic fluid,Insatability,Electrohydrodynamics, |
出版年 : | 2011 |
學位: | 碩士 |
摘要: | 奈米纖維是極為重要的奈米材料,具有良好的機械性質,在光電以及觸媒產業有很廣泛的應用。而電紡是目前唯一可以製造連續性奈米絲的技術,但由於其所牽涉到的物理機制非常複雜,且其成絲形態往往會受到實驗參數的影響,故此技術還停留在發展階段。在理論分析中,常以穩定性分析來探討電紡的動力行為,受制於各種模態擾動量的影響,會使奈米纖維有不同的成絲形態,例如:串珠狀與分岔等。
目前有關實驗參數控制的理論模型尚未發展完全,故本論文希望可以架構一個合理的數學模型,以基礎流體力學、電磁學、流變學,搭配線性穩定性分析來探討電紡絲的物理機制,以方便對奈米絲的成絲形態做初步的解釋。 電紡主要的控制機制是操作電壓,故在數學建模時,應該把軸向電場納入考慮,但由於黏彈性流體組成率與電場邊界條件使得方程式處理變得困難,所以目前尚未有人在下游處一併考慮軸向電場。此外,軸向電場會加速噴流,使得流場基態解會隨著下游變化而難以做穩定性分析。但有學者提議,若參數選擇在特殊的範圍,軸向電力和流體的應力已做抗衡,可以把加速的影響忽略,將速度場視為固定,本論文將用此近似法來做三維的線性穩定性分析。 Nanofibers are one of important nano-materials with good mechanical properties and wide applications in the catalyst and optoelectronic industries. Among various methods, Electrospinning is the only one that can produce continuous and uniform nanofibers. However, this technology is still developing because the process involves complex motion, affected by interaction between electric stress, viscoelastic force, and surface tension. In general, good morphology of nanofibers is unobtainable if the operating conditions are not appropriately chosen. A complete understanding of physical mechanisms is thus necessary for the improvement of the technique. So far, the theoretical study is still focused on the linear instability analysis because a complete analysis must include the nonlinear coupling between the rheological constitutive laws and Maxwell equation. Even so, the linear analysis can provide preliminary understanding of instability mechanisms. Previous works have revealed that the various undesirable morphologies (ex. bead-on-strings, branch) are actually resulted from the growth of nonaxisymmetric disturbances during the jetting process. However, the results are obtained by neglecting either the axial electrical field or the unrelaxed viscoelastic tension, which has caused quantitative disagreement when compared with experimental measurements. This paper aims to improve the existing mathematical model by taking both the effects of the axial electrical field and the viscoelastic tension into account. By this analysis, a deeper insight into the physical mechanisms during electrospinning process will be provided to qualitatively explain the formation of various microstructures of nanofibers. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/32151 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用力學研究所 |
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