陽極氧化鋁模板之製作及高分子奈米纖維之不穩定現象探討

Abstract

近年來，高分子奈米材料的製作及應用已經引起了各界科學家的重視，因其具有製作容易及表面特性易於調控等優點，而廣泛應用於藥物傳遞、太陽能電池或是感測器等領域中。陽極氧化鋁(anodic aluminum oxide, AAO)為最常使用於製作高分子奈米材料的模板，因為AAO具有高密度、孔徑大小均一的奈米孔洞，且可依照需求，調整孔洞大小、厚度及孔洞間隔，最重要的是製成容易、成本低廉等優點，在眾多模板中脫穎而出。 本篇論文主要分成兩個部分作探討:第一部分為陽極氧化鋁膜板與陽極氧化鋁線的製作與控制。我們利用草酸為電解液，以“二次陽極氧化法”製作出具有六方緊密堆積孔洞的AAO模板。利用磷酸做擴孔處理，擴孔時間及孔徑大小呈線性關係。隨著第二次陽極氧化處理時間增加，所得到的孔洞厚度也增加。利用指甲油作為保護層，將AAO開孔。因此，我們可以製作出孔徑介於33 ~ 83 nm，孔洞厚度至116 μm，孔洞通道開一端或兩端都開孔的AAO。最後將同樣的實驗參數應用在鋁線上，製備出孔洞通道垂直於鋁線表面且呈放射狀結構的陽極氧化鋁線。 第二部分為利用陽極氧化鋁膜板製作高分子奈米纖維及探討其熱退火後因雷利不穩定(Rayleigh instability)現象的形態轉變。我們利用AAO並以非溶劑法製作出poly(methyl methacrylate) (PMMA)奈米纖維，在沒有AAO孔洞限制及基板效應條件下，將PMMA奈米纖維置於非溶劑乙二醇(ethylene glycol)中進行熱退火處理，PMMA奈米纖維會因為雷利不穩定性而導致表面開始產生波浪狀起伏，最後轉變為PMMA奈米球以降低其表面能。由於高分子在溫度較高時黏度較低，因此在高溫加熱時的轉變時間會比在低溫加熱時還要快。我們也發現奈米球的大小與加熱的溫度並沒有直接的關係。

In recent years, the fabrication and application of polymer nanomaterials have attracted great attention because they are easy to fabricate and their surface properties can be well-controlled. Polymer nanomaterials have great potentials in applications such as drug delivery, solar cells, and sensors. The template method is considered to be one of the most effective methods to fabricate polymer nanomaterials. The main idea of the template method is to introduce the polymer materials into the pores of the template using polymer melts or polymer solutions. The nanomaterials, whose structures are controlled by the size and shape of the pores in the template, can be obtained after the removal of the template. The most popular material used as the template is anodic aluminum oxide (AAO) because of its high density and regular size of nanopores. The pore diameter, pore length, and pore-to-pore distance can be controlled by the electrochemical reactions. In addition, the fabrication process of the AAO template is simple and convenient. This thesis is divided into two main parts. The first part is to fabricate AAO templates and AAO wires. AAO templates with ordered pores are made by the second anodization method using a 0.3 M oxalic acid. The AAO template is placed in phosphoric acid to widen the pores to the desired pore size and the pore diameter is proportional to the widening time. The length of the pore increases with the second anodization time. Nail polish is used as a protective layer to open the pore and to obtain the AAO template with through pores. We can synthesize AAO templates with pore diameters ranging from 33 to 83 nm. The pore length is ~116 μm, and AAO templates with through pores can be obtained. In addition, we use similar experimental parameters to prepare cylindrical porous anodic aluminum (CPAA). The nanopores have radial configuration with hexagonal packed nanopores on the aluminum wire surface. The second part in this thesis is to study polymer nanofibers made from AAO templates and their structure transformation into nanospheres driven by the Rayleigh instability. We use AAO templates to prepare poly(methyl methacrylate) (PMMA) nanofibers by adding nonsolvent. The transformation process of the PMMA fibers is studied by annealing the fibers in ethylene glycol. The PMMA nanofibers are under thermal annealing without the confinement from the template and substrate. After the nanofibers are thermally annealed in ethylene glycol, which is a non-solvent for PMMA, the nanofiber surface undulate and transform into nanospheres to reduce the interfacial energy driven by the Rayleigh instability. The transformation time at higher annealing temperature is shorter than the time at lower annealing temperature because of the lower viscosity. The sizes of nanospheres are found to be independent of the annealing temperature.