Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3463
標題: Swelling and Elastic Modulus of Acrylic Acid-containing Dextran Hydrogels
丙烯酸聚葡萄醣水膠之膨潤性質與彈性模數性質的探討
作者: 陳偉揚
Chen, Wei-Yaung
關鍵字: pH-sensitivity;酸鹼敏感;Dextran hydrogel;Swelling ratio;Elastic modulus;聚葡萄糖水膠;膨潤性質;彈性模數
出版社: 化學工程學系
摘要: 
本實驗所規劃的聚醣類水膠材質為聚葡萄糖 (dextran) ,主要是利用glycidyl methacrylate (GMA) 與dextran進行轉酯化反應賦予此聚醣類主鏈帶有vinyl group。此vinyl group在一dextran分子上的數目可藉由GMA與dextran醣單元的反應莫耳比達到精準的控制。利用MA-dextran及acrylic acid (AAc) 於水相中進行自由基共聚合反應,以APS及TMEDA作為起始系統,製備的聚醣類水膠便具有酸鹼應答作用的應答型水膠,以達到保護藥物及藥物釋放,進而達到治療的目的。實驗中不僅利用FTIR求得AAc在dextran水膠中實際所佔的比率,並計算水膠中AAc的解離程度、Donnan Ratio、水膠內外之離子濃度差及水膠膨潤之離子化學位能差。發現因為此時水膠中解離之AAc會愈來愈多,使得水膠內外濃度差增加,引起水膠膨潤之離子化學位能會隨著pH值的增加而增加。在水膠彈性模數 (G) 方面,發現水膠的G值會隨著pH值而呈現先降後升的趨勢,此現象是很不尋常的,因為隨著水膠的膨潤造成水膠高分子彈性鏈濃度被稀釋的影響之下,所以彈性模數應該隨著膨潤的增加而減少。初步定性的推論這可能是因為水膠達到某一膨潤時,由於高分子鏈上的彈性鏈逐漸減少和被拉伸到極致的影響下,造成高分子鏈較堅硬 (stiffness) ,使得彈性模數增加。因此水膠彈性力的變化已不屬於高斯分佈之行為,在以理論分析水膠之膨潤行為時會產生偏差外,我們也利用non-Gaussian 彈性分佈的理論來定量的描述此種現象。而且我們也運用 inverse Langevin 函數和non-Gaussian entropy function來表示彈性模數的變化。當一個高分子鏈上具有的flexible unit,它的數目為無限大時 (n=∞),Gr (redused elastic modulus) 與 Vr (redused volume) 於雙對數圖中呈現一種線性的關係,並且斜率為 -1/3 ,這時高分鏈的行為遵循Gaussian彈性理論所推論出的結果;但當n 為一個有限值的時候,此時也有一種線性關係,而且斜率為 1/3,然而這時高分鏈的行為則遵循non-Gaussian彈性理論所推論出的結果。除此之外,我們還針對水膠膨潤或水膠受壓縮時造成flexible unit變化的影響,可以發現flexible unit會隨著水膠膨潤的增加而減少,也會隨著水膠所受壓縮的比率增加而增加。同時我們也計算出遵循高斯或非高斯理論的高分子彈性鏈造成的化學勢能,也發現高分子彈性鏈造成的化學勢能會隨著pH值的增加而增加。除此之外,也探討了緩衝溶液的離子強度對水膠膨潤性質與彈性模數性質的影響,可以發現水膠的膨潤似乎成為了彈性模數變化的主因,無論在低離子強度或高離子強度下彈性模數街有先減後升的現象,而在高離子強度時雖有上升但較不明顯,這可能是因為此時產生counterion condensation ,形成multiplets而造成彈性模數有稍稍上升的趨勢。

In this research, pH-sensitive dextran hydrogels were prepared by radical copolymerization of acrylic acid (AAc) with methacrylated dextran (MA-Dex). Ammonium peroxydisulfate (APS) and N,N,N',N'- tetramethylethylenediamine (TMEDA) played as an initiation system. The incorporated amount of AAc in hydrogels were measured by FTIR. Then the total ion concentration difference inside and outside the hydrogel based on the Donnan equilibrium theory was calculated. The the dissociation degree of AAc in hydrogels and the chemical energy caused of the difference of ion concentration inside and outside the hydrogel were calculated. It was clearly observed that the effect of the pH and the ionic strength effects change. The dominations and descriptions of the sensitivity of the swelling behavior of hydrogels to the ionic osmotic pressure were well. In addition, he elastic modulus of swollen hydrogels were measured by mechanical uniaxial compression. Moreover, the non-Gaussian behavior of effective chains was observed due to high swelling of polymer networks at high pH. In order to describe quantitatively the non-Gaussian statistics, the well known treatment based on the inverse Langevin function and non-Gaussian entropy function were introduced to interpret the change in the elastic modulus of elastically effective chains at high extents of swelling. The effect of the swelling degree of hydrogels and the ionic strength of buffer on the flexible units of elastically effective chains were described.
URI: http://hdl.handle.net/11455/3463
Appears in Collections:化學工程學系所

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