奈米柱誘發段鏈高分子自組裝行為之分子模擬研究

Self-Assembly Behavior of Block Copolymers Induced by Nanocylinders

紀霖恩(Lin-En Chi)

指導教授 ： 諶玉真

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201600394

摘要

兩性雙段鏈高分子能夠在選擇性溶劑下生成多種不一樣的結構，雙段鏈高分子在熔融態下也能自組裝成多樣不同的結構。螺旋結構在許多產業都很有發展的潛能，近年來，越來越多的研究專注於高分子的自組裝行為分析，唯獨雙段鏈高分子在溶液態系統下的自組裝螺旋行為較少被提及，仍具有一定難度及挑戰性。然而我們發現雙段鏈高分子在奈米柱上的螺旋包裝行為也許提供了一種可行性。在本研究中，我們利用耗散粒子動力學(DPD)模擬法，針對雙段鏈及三段鏈高分子在奈米柱誘發下的自組裝行為進行研究。
在系統中，除了片狀結構外，我們發現奈米柱的存在能夠誘導雙段鏈高分子，使其在表面上進行自組裝行為而生成螺旋結構。此外，濃度的高低又可將其分成圓柱形態與橢球型態。隨著高分子段鏈的增加，有趣的是我們可以觀察到橢球型態逐漸轉換為圓柱形態，然而當接近臨界值時，轉換速度增快，這時形成一緩衝區。我們也對高分子濃度、段鏈比例、段鏈與奈米柱間的作用力等對結構的影響進行探討，建立一完整相圖並發現其具有三相共存的現象，亦即在固定參數下，單股-單股螺旋結構、雙股-雙股螺旋結構、片狀結構皆有機會生成。而為了排除週期性邊界條件影響模擬結果的疑慮，也建立一系統，使其能自組裝成特有的環狀結構。
最後，我們以相似手法運用在三段鏈高分子的系統中，發現奈米柱仍能提供誘導能力使其自組裝成螺旋結構。在固定濃度及作用力參數下，整理出兩張相圖用以觀察段鏈比例對自組裝形態的影響。不同的是，三段鏈的系統沒有三相共存的特點，反之在相圖中相同的結構皆較為靠近，顯示受段鏈比例的影響不大，但在一定範圍內較易生成特定結構。最特別的是，在特定參數下，濃度效應竟也能影響其自組裝結構。
我們可以得知在段鏈高分子的系統中，只要借助奈米柱的誘導效應，再搭配注入不良溶劑及至少有一段鏈對奈米柱具備一定吸引力，便可自組裝成螺旋結構以作其他利用。我們的研究結果或許可以對那些有意建立段鏈高分子溶液自組裝成螺旋結構相關實驗的學者們開啟另一扇窗。

關鍵字

自組裝 ； 段鏈高分子 ； 奈米柱 ； 螺旋

並列摘要

Amphiphilic diblock copolymers can self-assemble in a selective solvent to form various structures. Diverse morphologies of self-assembly can also be observed in the polymer melt of diblock copolymers. The helical structure has great potential for many applications. Nonetheless, the helical structure of diblock copolymers in polymer solutions has seldom been reported and the formation of helixes of diblock copolymers in a selective solvent is still a challenge. However, helical wrapping of a nano-cylinder provides a possibility for the formation of helix of diblock copolymers. In this study, DPD simulations are performed to explore the self-assembled morphology of diblock and triblock copolymers onto a nano-cylinder.
It is found that the presence of the nano-cylinder is able to induce helical wrapping of diblock copolymers. Helical ellipsoids and helical toroid appear. Moreover, the morphology of the helical aggregate changes with the polymer concentration. With increasing the number of polymers N, helical ellipsoids transform into helical cylinder as the polymer concentration exceeds a critical value. The influences of polymer concentration, block compositions, and the interaction between polymer and nano-cylinder on the morphology are investigated. As a result, a morphological phase diagram is constructed.
It is also found that the presence of the nano-cylinder has the ability to induce helical wrapping of triblock copolymers. With fixed number of polymers and interaction strengths between polymer and nano-cylinder, two different morphological phase diagrams are presented for triblock copolymers with different compositions. Additionally, it is also discovered that the concentration effect on morphology for triblock copolymers is different from that for diblock copolymers. It may transform into other conformation with different number of polymers N. Our simulation results may shed some light on the experimental development for the formation of the helical suprastructure of diblock and triblock copolymers in solutions.

並列關鍵字

self-assembly ； block copolymer ； nanocylinder ； helical

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