兩性分子溶液相行為之自洽場研究－以星狀共聚高分子與植烷三醇分子為例

Abstract

近年來，可溶性塊狀共聚高分子(lyotropic block copolymer)自組裝而成的各種精緻結構受到廣泛的研究與討論，對於奈米材料的製備與應用開啟了一條新途徑，在日常生活中，我們常可見到可溶性塊狀共聚高分子以及界面活性劑的蹤跡，其廣泛應用於身體產品的助溶劑與穩定劑中，在藥物運送膠囊的開發上也獲得大量注目及研究。 本論文包含兩個研究主題，我們利用自洽場理論(self-consistent field theory; SCFT)來研究星狀共聚高分子以及植烷三醇(phytantriol)這兩種不同的雙親性分子之相行為，此兩種分子尺寸有極大的差異，星狀共聚高分子為巨分子而植烷三醇則為小分子型界面活性劑，共聚高分子的雙親性質與生活中常見的界面活性劑非常相似，然而共聚高分子的鏈段長度卻是界面活性劑的百倍長以上，這使得高分子比界面活性劑更適用於平均場理論的計算，然而仍有研究者利用自洽場理論研究界面活性劑或脂質的相行為，因此在本篇論文中，我們利用自洽場理論來計算兩個系統:其一為可溶性星型塊狀共聚高分子在不同溶劑系統下的相行為，其二則是植烷三醇水溶液之相行為，前者目的在於想了解高分子結構以及溶液選擇性對於自組裝結構的影響，後者目的則在於欲建構植烷三醇的自洽場理論模型來解釋實驗結果，並提供建議給後續的藥物毒性研究。 本文的第二及第六章內載有AnBm共聚高分子溶液以及植烷三醇水溶液之自洽場理論推導，我們將Matsen與Schick兩位先生在1994年發表的自洽平均場計算方案做延伸，此演算在當時是用於研究雙鏈段線性高分子在熔融態的相行為並利用光譜法來求解配分函數，在本文中我們發表的演算法適用於計算多臂塊狀共聚物加入溶劑後之相行為以及擬植烷三醇結構分子加入水溶液之相行為。 在第三章中，我們計算了幾個A1Bm星狀共聚物在中性與弱選擇性溶劑中的常態相。藉由改變B高分子的分支數目以及溶劑濃度，我們利用數值方法計算出A1Bm星狀共聚物的相圖並且找出其相變濃度；本文主要探討溶劑濃度、選擇性、以及高分子自身結構對於自組裝微結構所造成的影響。在固定的高分子長度以及A團塊的體積分率下，擁有較多分支的星狀高分子將導致高曲率自組裝結構之形成；若加入大量無選擇性的溶液，原低曲率結構亦會朝向高曲率產生變化；若加入親B團塊的溶液，則會助長分子不對稱性，在低溶液濃度下仍能產生高曲率結構；這些相變行為可利用稀釋近似(dilution approximation)以及臨界堆疊參數(critical packing parameter)來解釋。 本文第四章到第七章在探討植烷三醇水溶液，與其添加二棕櫚醯磷脂絲氨酸(dipalmitoyl phosphatidylserine, DPPS)之水溶液，以及製備成cubosome粒子後所衍生的各種相行為，實驗細節將在第五章詳述。在此我們主要利用小角度X光散射來建構植烷三醇水溶液的相圖，並且確認添加DPPS以及製備成Cubosome將造成相變；在植烷三醇水溶液相圖中，只有反轉相(inverted phase)以及層相(lamellar phase)會產生，反轉相包含有微胞相(micelle)，螺旋二十四面體(gyroid)，雙鑽石連續結構(double-diamond)，以及六角堆積圓柱結構(hexagona-packed cylinder)，我們進一步建構了擬植烷三醇分子在水溶液中的自洽場理論，並期望發現穩定相區域，在本計算中，分子間作用力是利用FH/Hansen模型來模擬溫度對作用力之影響，計算分子作用力必須先得知分子的溶解度參數，可由實驗數據得知；限於擬植烷三醇分子結構的複雜性，在此自洽場理論計算中，目前僅發現穩定的反轉微胞相以及層相。

Nowadays, lyotropic block copolymers and surfactants have been extensively applied whether in our daily life or in lab experiments. One can found their presence from the solubilizer for the water immiscible drugs, the stabilizer for the emulsions in our daily body care products, to the novel drug delivery capsules. These amphiphilic molecules have been an inevitable existence for decades. There are two topics in this thesis. The self-consistent field theory (SCFT) was applied to study the phase behavior of two different amphiphilic molecules, the star block copolymers and the phytantriol molecules. The molecular sizes between them are with large difference. The block copolymer is the macromolecule while the phytantriol is the small surfactant. The amphiphilic peculiarity of lyotropic block copolymers lets them play a similar role as small surfactants do in the solution, but the long chain nature of copolymers allows it to become easier to use the SCFT. However, there are still researchers who applied SCFT to the surfactant or the lipid phase study. Thus we use the SCFT in this thesis, in order to study the phase behavior of two systems: the A1Bm star copolymers blended with neutral or weak selective solvent, and the phytantriol water solution. For the star copolymer case, the main purpose is to discuss the star copolymer architecture as well as the solvent properties affecting the self-assembling behavior. As for the phytantriol case, we want to construct a SCFT model to match the experimental phase diagram for the future drug toxicity research. The theoretical derivation of the SCFT for AnBm copolymers with solvent and for the phytantriol water solution was presented in chapter 2 and 6. We extended the SCFT scheme from Matsen and Schick to solve the partition function by spectral method. This scheme was developed for studying the polymer melt phase behavior in the beginning. We presented the SCFT calculational algorithm for the block copolymers within a specific class of multiple arms chain architecture in the chapter 2, and for the phytantriol-mimic architecture in the chapter 6. In the chapter 3, we calculated the common mesophases for the A1Bm star copolymers. By changing the arm number of B or solvent property, we constructed numerically the phase diagrams and located the phase boundary between the lamellar, the hexagonal and the micelle related phases. These formatted phases were discussed from two points of views: copolymer architecture, and the solvent selectivity. In the constant copolymer segments (N=200) and A-block volume fraction (fA=0.4), A1Bm star copolymer with higher arm number (m) can lead to the easier formation of the higher curved phases. When large amount of the neutral solvent was added, the phase changed toward the higher curved one as well. Weak B-selective solvent enhances the asymmetricity further so that makes the phase change more easily at the lower solvent concentration. The phase transition in the neutral solvent was explained by the dilution approximation, while the transition caused by the selective solvent or by the architecture was explained generally by critical packing parameter. The phase study for the phytantriol water solution, its dipalmitoyl phosphatidylserine (DPPS) derivation, and the phytantriol cubosome was presented from chapter 4 to 7. The experimental details for the phase study were depicted at the chapter 5. We used the small angle x-ray scattering (SAXS) to construct the phase diagram of the phytantriol/water system, and to find the phase changed after the DPPS addition or the cubosome processing. Only inverted phases and lamellar phase were presented in the phytantriol/water system, including the inverted micelle, inverted gyroid, inverted double diamond, inverted hexagonal packed cylinder and the lamellar phases. The SCFT for the phytantriol/water system was built in order to find the stable phase region and only find the stable lamellar and micelle phase for now.