利用模板法製備之高分子奈米材料的形態控制

Abstract

近幾年由於奈米科技的發展漸趨成熟，已有許多製作奈米結構的方法被發表，其中最值得注意的為利用多孔性陽極氧化鋁的「模板法」，本論文分為兩大主題，第一部分在第三章「高分子在陽極氧化鋁模內藉由非溶劑沉積的限制效應」中，我們將探討當高分子材料在多孔性的模板孔洞裡時，經非溶劑影響下其形態的變化，這一簡單的參數之前從未有人仔細探討過但卻是關鍵的步驟，有無加入非溶劑的差異就可能造成結果些許的不同，我們使用最常見的水當作高分子的非溶劑，加入已有聚甲基丙烯酸甲酯和二甲基甲醯胺的高分子溶液(5wt.% PMMA/DMF solution)存在於陽極氧化鋁anodic aluminum oxide (AAO)的孔洞中，發現水會使聚甲基丙烯酸甲酯在其中聚集析出到孔洞中間，等到二甲基甲醯胺溶劑擴散後高分子固化成型，聚甲基丙烯酸甲酯的奈米球或是奈米柱於是獲得，此形變的驅使力為「雷利不穩定性」，在轉換過程因高分子和各介面表面積變大而使整個系統的表面能降低達到穩定態，從中我們可以控制濃度、溶劑蒸發時間來控制最後奈米柱(球)的長寬比，且當沒有水的加入時，高分子固化覆蓋在陽極氧化鋁模的管壁上形成空心的奈米管，此兩種不同的結果證實非溶劑對高分子溶液的影響在某些系統條件中是有一定程度的，此外這也是一個簡單做奈米球的方法，運用簡單加入非溶劑(水)的步驟，搭配氧化鋁奈米孔洞的限制，我們可以得到大小均一的奈米球。 第二部分為第四章「溶劑蒸氣誘導高分子奈米結構之研究」，由於「模板法」之中又分為兩種常見濕潤模板的方式，一為將高分子配成溶液的「溶液法」(solution method)，另一為經由熱力使高分子融化的「熔化法」(melting method)，此兩種方法都已行之有年也相當普遍，但卻都有各自無法避免的優缺點，而在第四章中我們將提出另一個利用溶劑蒸氣驅使的「溶劑退火法」(solvent annealing)，利用高分子在其良好溶劑的蒸氣環境中，可以澎潤而具有流動性後進而濕潤模板孔洞形成奈米結構，發現此方法不僅可以改進「溶液法」無法有效控制所得奈米管柱長度的問題，也兼具了「融化法」可調控結構、使內部分子鏈排列良好的特性，且不管高分子的分子量，只要透過簡單更換不同溶劑的方式就可以改變結構，和另兩種方法相比，奈米結構的大小或是長度的控制也相當不錯，經由這一新的製程方法，可以更加了解到高分子在濕潤模板時的機制，往後也將朝著更多有特殊性質的高分子材料的應用前進。

Adding nonsolvent into a polymer solution is a common technique to prepare polymer nanostructures. But usually polymer nanostructures made by this method has ill-defined sizes. In the third chapter, we study the fabrication of polymer spheres and nanorods by adding nonsolvents into the polymer solution confined in the nanopores of anodic aluminum oxide (AAO) templates. Water (nonsolvent) is added to a PMMA solution in DMF while the AAO template is present. The nonsolvent causes the polymer solution to be isolated and form nanospheres or nanorods after the evaporation of the solvent. The aspect ratio of the polymer nanorods depends on the solution concentration. The morphology of the polymer nanostructures also depends on the evaporation time of the polymer solution before adding the nonsolvents. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh-instability-type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained. Another work we do is about the wetting process in fabrication of nanostructures by AAO template. For wetting porous templates to produce polymer nanomaterials, two common ways to introduce the polymers into the nanopores of the porous templates are the solution method and the melt method. Although the solution method and the melt method are widely used in making different polymer nanomaterials, there are still some disadvantages by using these two methods. To overcome the above problems for the melt and solution methods and to allow more types of polymers to be used in the template method. In the fourth chapter, we develop a different method to make polymer nanomaterials by wetting the porous template using solvent annealing. In the solvent annealing process, the polymer gain mobilities by exposing the sample in the vapor of an organic solvent without heating the polymers, so that they are able to wet the channels of the templates. In the solvent annealing method, we find that, even for the same polymers, the nanostructures (nanorods or nanotubes) of the polymers can be controlled by changing the solvents used for the solvent annealing process. This solvent annealing method is simple and compensatory to the other two methods. The size and morphology of the polymer nanomaterials can be controlled readily. This study adds a new branch of research directions in the field of template-based nanomaterials. Not just for polymers, the solvent annealing method is also expected to be applied to prepare other functional materials such as metals or inorganic nanomaterials which using polymers as host materials. Therefore, different applications based on functional nanomaterials can be benefited from this study.