高分子薄膜中的週期相分離圖案發展及其中奈米線的圖案排列

吳坤樺(WU, KUNHUA)

指導教授 ： 呂世源 ； 陳信龍

國立清華大學/工學院/化學工程學系/博士(2006年)

https://doi.org/10.6843/NTHU.2006.00042

摘要

本論文討論高分子薄膜內的週期相分離形態的形成與發展，和分佈在高分子薄膜內的奈米線的圖案排列現象。首先以兩不互溶之聚苯乙烯（PS）和聚乙烯吡咯烷酮（PVP）高分子材料形成的聚摻薄膜為模型系統，探討銀奈米線的引入對相分離的影響。研究中使用的銀奈米線，是以陽極氧化鋁模板（AAO）法經由電化學沉積的方式製備出來的，其長度和直徑分別為10μm和300nm。在較高奈米線含量時（10%），銀奈米線會交錯在一起並選擇性分佈在PVP相中，而奈米線經由硫醇分子疏水改質後，則改為選擇性分佈在PS相中。另外，在較低奈米線含量時（5%），奈米線分散在PS和PVP相界面附近，並使相分離形態產生重大的改變，形成連續相形態。第二，在以PS/PVP/氯仿溶液在平坦基板上塗佈之旋轉塗佈薄膜上，我們發現條狀相分離形態的出現。這樣子的非均向性圖案同時具有高度和組成變化，並歸因於由Marangoni不穩定所驅動的。在溶劑快速揮發的情形下，相分離產生的PS和PVP會流向特定的地方。另一方面，以溶液成膜法在傾斜基板上塗佈出的PS/PVP聚摻薄膜，在Marangoni不穩定的影響之下，相分離形態可以呈現出規則陣列圖案或平行條狀的相分離圖案。以上兩種圖案都被證明與高分子溶液濃度和薄膜厚度有關，我們並將此兩個變數組合成一相關係數，來研究在不同溶液濃度下的相分離形態。第三，我們展示了在旋轉塗佈高分子膜內，奈米線的分布也會受到Marangoni不穩定的控制，組合成平行的條狀奈米線圖案，與單純高分子薄膜上的條狀隆起圖案相類似。奈米線被發現會集中到高分子條狀圖案的低窪處，以平衡液膜表面上不均勻的表面張力分布。奈米線條狀圖案與高分子溶液濃度、旋轉轉速、奈米線含量和高分子種類有關。我們將奈米線在不同高分子中的凡得瓦吸引力相對強度估算出來，發現在只有聚集成團的奈米線出現，而沒有奈米線條狀圖案出現的高分子薄膜中，奈米線的相互吸引力確實是較強的。我們證明這個奈米線圖案是Marangoni效應、離心力和凡得瓦吸引力交互作用下的結果。

關鍵字

相分離圖案 ； 馬蘭格尼對流 ； 銀奈米線 ； 高分子薄膜 ； 旋轉塗佈

並列摘要

This thesis dicusses the formation and development of periodic patterns of separated phases in polymer thin films, and also the patterned nanowire distributions in polymer blend thin films. First, the preferential partition of silver nanowires in thin films of PS/PVP blends, that induces drastic blend morphology variation, was reported. The silver nanowires were fabricated with the anodic aluminum oxide templating method, and had a diameter of 300 nm and length of 10 mm. At a higher nanowire loading of 10%, the silver nanowires were entangled and selectively concentrate within the continuous PVP domain. If surface modified by thiols carrying hydrophobic tails, the silver nanowires became hydrophobic and preferred to stay within the discrete hydrophobic PS domains. At a lower nanowire loading of 5%, the nanowires stayed non-entangled and concentrated at regions near the interfaces of the PS and PVP phases, which induced the formation of interconnected PS domains.
Second, patterns of parallel strips were observed in thin films spin cast from the PS/PVP/chloroform solution on un-patterned substrates. The formation of anisotropic patterns, manifested not only in thickness variation but also in composition variation, was found to be driven by the Marangoni instability, with the PS and PVP streams flowing toward the preferred regions as the phase separation induced by solvent evaporation proceeded. On the other hand, periodic patterns were obtained for PS/PVP blend films, solution cast on tilted glass substrates. Regular arrays of the separated phases and strip patterns of separated phases were observed. The initial viscosity of the polymer solution and the thickness of blend films were lumped into one single parameter to study the phase morphology development at various initial polymer solution concentrations.
Third, parallel striations made of silver nanowires were formed through the Marangoni instability induced during spin cast of nanowire/polymer solutions. The silver nanowires were found to concentrate at the valleys of the striation pattern to balance the non-uniform surface tension distribution in the polymer thin film. The resulting nanowire striation patterns were found to depend on polymer concentration, rotation speed, nanowire loading, and polymer characteristics. The van der Waals interactions between silver nanowires suspended in several different polymer solutions were estimated to correlate with the quality of the nanowire striation pattern achieved for different polymers. Nanowire agglomeration occurred in polymers giving large van der Waals interactions such that no nanowire striation pattern was formed in these systems. The distribution of nanowires in the spin-cast polymer thin films was found to be governed by the coupling competition among the Marangoni convection, van der Waals attractive forces, and centrifugal force.

並列關鍵字

phase separation pattern ； Marangoni convection ； silver nanowire ； polymer thin film ； spin coating

參考文獻

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