以耗散粒子動力學法研究雙段鏈星狀高分子之型態

Abstract

本論文分為兩部份，第一部份我們利用耗散粒子動力學法模擬heteroarm star copolymer（A7B7）在共同溶劑（common solvent）以及選擇性溶劑（selective solvent）中的型態。結果顯示單一星狀高分子在共同溶劑中由於A、B鏈段間不相容以致於在溶劑中形成A、B鏈段各自向外伸張的髮狀 Janus-like的型態，而在選擇性溶劑中，因為B鏈段不親溶劑，因此B鏈段傾向於聚集成球狀團聚體而形成球-髮狀Janus型態。兩heteroarm星狀高分子在共同溶劑中會互斥；而在選擇性溶劑中則會相互吸引聚集，此種現象衍生至多分子系統有利於多分子微胞（multimolecular micelle）的形成。另外，多分子系統的聚集行為受到手臂數的影響並不明顯，在固定星狀高分子濃度的情況下微胞的平均尺寸隨著手臂數的增加無明顯的趨勢；系統濃度增加則會使得微胞的尺寸增大，同時微胞數量隨之減少。 第二部分我們研究兩種類型雙段鏈星狀高分子(AB)m、(BA)m在選擇性溶劑中的型態。在單一分子系統，(AB)m型星狀高分子中的B鏈段會在分子外圍形成數個聚集體，隨著B鏈段長度的增加，B鏈段間相互聚集的傾向越強，到達一定長度後所有B鏈段匯聚成一團而形成Janus-like型態；當鏈段長度固定，改變B鏈段與溶劑之斥力參數，隨著斥力aBS增加，B鏈段相互聚集的傾向也越強，到達一定斥力強度後B鏈段會聚集成一團而形成Janus-like型態。(BA)m型星狀高分子在選擇性溶劑中則會形成分子內微胞。兩(BA)m型星狀高分子在溶劑中存在的是斥力，彼此不會相互聚集，而(AB)m型星狀高分子則會相互吸引聚集。在多分子系統，(AB)m型星狀高分子會因B鏈段長度不同而有不同的聚集型態，當B鏈段到達一定長度便會形成多分子微胞（multimolecular micelle），微胞的大小則會隨著濃度的增加而有增加的趨勢。

The morphology of heteroarm star copolymer (AmBm) and blockarm star copolymers (AB)m and (BA)m are investigated by dissipative particle dynamics (DPD). For a heteroarm star copolymer (AmBm) in a common good solvent, with repulsive interaction between A- and B- arms, hair-like Janus conformation is observed. However, in a selective solvent, as A being solvophilic and B being solvophobic, B-arms tend to form a spherical aggregate and single AmBm star copolymer now assume hair-ball Janus conformation. Interactions between AmBm stars in common good solvents are repulsive while AmBm stars in selective solvents are attractive. Thus multi-molecular micelles can be found for AmBm stars in selective solvents. The size of the micelle increases as the number of star arms (m) increases at constant molecular concentration. Also, for fixed m, the size of the micelles increases and the number of aggregates decreases as the volume fraction of the AmBm star increases. For a blockarm star copolymer of (BA)m type in a selective solvent, since the solvophobic B-blocks situated in the inner part of the star, intramolecular micelles are observed. (BA)m type star copolymers repel each other, thus it is quite difficult for intermolecular micelles to form. For a blockarm star copolymer of (AB)m type in a selective solvent, different numbers of aggregative domains develop on the outer rim of the star. The tendency of B-blocks to aggregate enhances as the length of B-blocks (lB) or the repulsive interaction between B-blocks and solvents (aBS) increases. This difference in the ability for B-blocks to aggregate greatly affects the conformations of the multi-molecular micelles.