以耗散粒子動力學法研究三段鏈星狀高分子之型態

Abstract

在本論文中，我們利用耗散粒子動力學（DPD）來探討三鏈段共聚合物（ABC triblock copolymer）的在稀薄水溶液中的型態。我們主要研究的對象有兩大主軸：線性（linear）、星狀（star）三鏈段共聚合物。我們分別改變兩者的濃度或親水部分的鏈段長度，來觀察聚合物之型態變化。在模擬的結果中，我們發現改變濃度時，無論聚合物分子結構是線性或星狀，聚集體的大小是隨著濃度增加而增大。而在改變親溶劑鏈段長度時，則發現線性三段鏈共聚合物之微胞大小會隨著親溶劑鏈段長度變長而變小，星狀三段鏈共聚高分子則是先隨親溶劑鏈段長度增加而增加，隨後去呈現下降的走勢。在三段鏈線性共聚高分子在稀薄水溶液中出現了core/shell/corona 的微胞型態；而三段鏈星狀共聚合物則是出現了節蟲（segmented worm ）型態，這些結果都與文獻中用TEM 所觀察到的型態吻合。顯示我們能成功的利用DPD 方法模擬出三段鏈共聚高分子之型態。此外我們還將分子結構調整為ACB-type、BAC-type 三段鏈線性高分子，在這兩個系統中我們觀察到skin-layer micelle、bicore micelle、sandwich micelle等，進一步的利用DPD 法對高分子型態做預測。

Mutually immiscible triblock copolymers are able to form various multicompartment micelles. Exploring their morphologies involves a large parameter space, including chain architecture, block length, and concentration. However, DPD simulation provides a relatively cheap and fast approach to predict possible morphologies. The complex structure within the multidomain micelle can be easily examined. In this work, we observe discrete micelles and 'segmented worm'micelles formed by miktoarm star OEF, which are consistent with the experimental results. The former consists of a F core, surrounded by a few E nanodomains. In general, two E nanodomain are found on the top and bottom of the F core to form 'sandwich' micelles. The O blocks emanate from the E-F interface and curl around to protect the hydrophobic core. The latter displays an elongated, wormlike structures.The worms are layered with alternating section of F and E blocks along the long axis. The O coronas are shared by E and F layers to shield them from the highly unfavorable exposure to water. The segmented worm micelle is always formed for star (x-6-7) as long as the polymer concentration is high enough. The onset concentration for the formation of segmented worm micelles is increased with the hydrophilic O block length. When the hydrophilic O block is large (x=20), the O block screen the hydrophobic core effectively and the sandwich micelles can survive at higher concentration. On the other hand, for stars with shorter O blocks (x=10), the fluctuation of O concentration in the corona may expose the hydrophobic core from time to time. As a consequence, in forming a segmented worm, the different sandwich micelles are able to share their O coronas. When the concentration is even higher, the segmented micelles may join together to form segmented network. In addition to miktoarm star, various morphologies of multicompartment micelles can be disclosed by linear triblock copolymers OEF, OFE, and EOF. For linear OEF (x-6-7) triblocks, the CSC structure can be evidently identified with the F core, E shell, and O corona. Nonetheless, the spread of the E blocks on the surface of the F core is not uniform due to E-F incompatibility. As the O block (x) is increased, the aggregation number of the micelle declines. For linear OFE (x-7-6) with shorter O blocks, the E blocks form a core that is surrounded by an incomplete skin layer of the F block. Since the O blocks protect mainly the F skin, part of the E core is exposed to water. However, when the O block is long enough to curl around to shield the E domain, the core consists of two separate but adjacent domains (E and F). When the concentration is high enough, the sandwich micelle (F-E-F) is formed by merging two F skin layer micelles. Its formation can remove the exposure of the E core of the skin layer micelle to water. For linear EOF (6-x-7) with longer O blocks, a micelle with two neighboring E and F layers is shielded by the O loops. However, as the O block is too short, only the combination of several two-layer micelles can provide enough protection by the O blocks. Consequently, segmented worm micelles are formed.