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利用分子動力學模擬全氟磺酸形態和結構構象之研究

Molecular dynamics simulation study of Nafion morphology and structure conformation

作者:郭純萍
畢業學校:國立中山大學
出版單位:國立中山大學
核准日期:2016-01-12
類型:Electronic Thesis or Dissertation
權限:Copyright information available at source archive--National Sun Yat-sen University....

中文摘要

由於全氟磺酸聚合物不易結晶,再加上其晶體與離子區域的複雜性,導致全氟磺酸的結構已經有很長的一段時間具有爭議性。Gierke團隊,根據小角度x-ray散射之研究進一步假設全氟磺酸有似反微胞之構型。這些微胞彼此藉由一個又窄又短的通道互相連結,運輸水分子。而此一假設為目前最廣泛引用的模型。但到目前為止,全氟磺酸聚合物並沒有公認的形態結構,這也使得我們想進一步去探討其真正的結構。
在本研究中,我們利用分子動力學模擬短鏈的全氟磺酸單體在不同水合數下的運動情形,並將其單體彼此互相接近下產生新的鍵結,而這些鍵結促使全氟磺酸單體聯結成一個不規則的網狀構形。為了比較修改鍵結前後兩系統的差異,我們分析平衡後的兩系統的體積﹑密度﹑徑向分布函數﹑擴散係數……等。而這些分析結果也明確顯示兩系統有所差異。

英文摘要

A widely accepted model for the solid-state structure of Nafion has not been given due to the low crystallinity and complexity of co-organized crystalline and ionic domains. This complex phase-separated morphology has been the target of several investigations which led to different models. The cluster-network model of Gierke et al. can be considered as the most widely referenced model. Based on small-angle X-ray scattering (SAXS) studies and several further assumptions, the model proposes that there are clusters of sulfonate terminated side chains that are organized as inverted micelles. These micelles are interconnected by a network of short and narrow channels which allow water and ion transport. So far, Nafion polymer morphology is has not be recognized. It makes us go further to explore its true structure.
In this study, we use molecular dynamics simulation to investigate the movement situations of short chain Nafion monomers at various levels of hydration. When the distance between two Nafion monomers is enough close, we generate the new Netted of them. These new Netted makes Nafion into an irregular net configuration. In order to compare the difference between netted and free system, we analyze the RDF volume, density, diffusion coefficient and radial distribution function of the two systems. These analysis results also clearly show the difference of two systems.

 

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