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標題: | 以分子動力學研究添加多價離子對聚甲基丙烯酸
稀薄溶液的影響及當中水分子的結構與動態行為 Structure and Dynamics of Water Surrounding the Poly(methacrylic acid) (PMAA) in the Presence of Multivalent Salts: A Molecular Dynamics Study |
作者: | Yong-Ting Chung 鐘勇庭 |
指導教授: | 黃慶怡(Ching-I Huang) |
關鍵字: | 分子動力學,聚甲基丙烯酸,聚電解質,架橋效應,屏蔽效應,徑向分佈函數,振動頻譜, MD,PMAA,polyelectrolyte,bridging effect,screening effect,radial distribution function,vibrational spectrum, |
出版年 : | 2007 |
學位: | 碩士 |
摘要: | 利用電腦模擬及理論計算,針對特定的聚電解質系統進行計算,以得到系統的各項結構相關性質及交互作用力等交互行為的數值參考資料。進一步了解聚電解質結構及系統中各交互作用行為間的關係。
我們在一稀薄水溶液中PMAA(poly (methacrylic acid))聚電解質系統額外添加鹽類(CaCl2),當系統中加入金屬離子時,高分子的構形會隨離子價數提升而趨向蜷曲,導因於離子價數提高時,凝聚至高分子鏈上的離子比例會增加,並且產生的架橋效應比例也會提升。但當添加鹽類離子價數大於聚電解質所帶的電荷,則會因為聚電解質上有著過多的鹽類離子,這些離子的靜電排斥效應,將使得高分子鏈漸漸地再伸展開來。 在此之前有關真實水分子系統的研究並不多,添加鹽類離子所造成的屏蔽效應(screening)雖然是已知的現象,但很少以MD來進行模擬。我們採用全原子模型,在聚電解質溶液系統置入真實的水分子,雖然會大幅增加電腦運算的時間,但可更確切地了解水分子的地位及對系統的影響。 藉由徑向分佈函數分析和形貌圖形觀察,我們發現水分子與COO-之間的平衡距離比一般氫鍵小,證明兩者之間存在強大的交互作用力,水分子藉由此作用力會在高分子鏈上產生特殊吸附排列行為,進而對聚電解質局部構形產生很大的穩定作用。針對不同吸附條件下的水分子進行動態行為分析,發現當水分子被COO-或離子吸附時,會使水分子整體的擴散變得緩慢,並使氧原子和氫原子的振動頻譜產生改變。 By doing computer simulations and theoretical calculations on specific polyelectrolyte chain systems, we obtain reference values for structure related properties and interactions of the system. By this, we can further understand the structure of polyelectrolyte chain systems and the relationship between different interactions in the system. In a dilute aqueous solution, we add a salt (CaCl2) to the PMAA (poly (methacrylic acid)) polyelectrolyte chain system. When metal ions are added to the system, the conformation of the polymer will tend to collapse with the increase of the ion valence. This is due to the increase in ratio of ions condensed on the polymer chain as ion valence increases, and therefore the ion-bridging effect ratio increases as well. However, when the valence of added salt ions is larger than the charge of the polyelectrolyte chain, the polymer chain will gradually stretch out again, as there will be excess salt ions on the polyelectrolyte chain, which creates electronic repulsion. Before now, there have been few studies on real water molecule systems. Although the screening effect of added salt ions is a known phenomenon, it has seldom been simulated with MD. We investigate by using all-atom simulations. Real water molecules are added to the polyelectrolyte chain solution system and treated explicitly. Although this greatly increases the time needed for computer calculations, it can give more precise understanding of the position of water molecules and its effect on the system. By radial distribution function analysis and schematic observation, we find that the equilibrium distance between water molecules and COO- is smaller than the usual hydrogen bonds, proving that there exists a strong interaction between the two. By this interactive force, water molecules exhibit special adsorption arrangements, thus having strong stabilization on the polyelectrolyte chain conformation. Analysis of dynamics of water molecules under different adsorption conditions indicates that when water molecules are adsorbed on COO- or ions, the overall diffusion of the water molecules becomes slow, and changes occur in the vibrational spectroscopy of oxygen and hydrogen atoms. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28192 |
全文授權: | 有償授權 |
顯示於系所單位: | 高分子科學與工程學研究所 |
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