利用耗散粒子動力學探討A-block-(B-graft-C)線性梳狀共聚合物的相行為

Abstract

我們運用耗散粒子動力學模擬A-block-(B-graft-C)梳狀共聚合物的相行為，此篇論文中我們排除了接枝比例所帶來的影響，假設梳狀共聚合物中每一個B粒子均接上一個C粒子。藉由改變作用力參數、組成與聚合度，我們成功的建構A-block-(B-graft-C)共聚合物一系列的相圖，並發現到來自A-線性端與BC-梳狀端所形成的二種等級特徵尺寸共存的微結構。首先藉由aAC = aBC值與aAB值的改變可以觀察到微結構的衍變，甚至進一步發現到結構內有結構的階段性結構。除此之外，我們更由聚合度與組成的關係發現到兩種等級特徵尺寸共存的微結構與BC-梳狀端的鏈段長度息息相關，當BC-梳狀端的鏈段長度較短時，其B成分均存在於A區塊與C區塊的界面中；當BC-梳狀端的鏈段長度足夠長時，我們則可以發現到BC分離的小尺寸層狀垂直於大尺寸結構的階段性結構。因此，隨著組成fA的增加，形成一系列階段性結構的聚合度也隨著上升。最後，我們更利用作用力參數aAB值、aAC值、aBC值的改變發現到aAC值較低時，aBC值提高時無法觀察到二種特徵尺寸的微結構，主要是因為A與B十分相容無法造成A-線性端與BC-梳狀端的大尺寸分離；aAC值較高時，由於A對B以及A與B對C不相容時造成A-線性端與BC-梳狀端的大尺寸分離與BC-區塊內的小尺寸分離，甚至當aAC值、aBC值很高的情況下造成BC鏈段越來越伸展，導致在二種特徵等級尺寸共存的微結構中會造成大尺寸微結構的轉變。由以上的所有結果也顯示出作用力參數、組成與聚合度對於階段性結構的形成均扮演著不可或缺的角色。

We employ the dissipative particle dynamics (DPD) to examine the microphase separation of A-block-(B-graft-C) copolymer. In this study, the effects caused by connect of ratio were reduced, and it was hypothesized that in the linear-comb copolymer, every B bead were attached with a C bead. Taking advantage of changing interaction parameter, composition, and degree of polymerization, we succeeded in constructing a series phase diagram of A-block-(B-graft-C) copolymer. Moreover, we found a hierachical structure with two length scales, i.e., the so-called structure-within-structure, can be induced by A-coil block and BC-comb block. First of all, by vary the value of interaction parameter, aAC = aBC and aAB, we can observe the morphology transition, or even find the hierachical structure. In addition, we also discovered that hierachical structure and the length of the BC-comb block are closely related by looking into the relation between degree of polymerization and composition. In other words, when the length of the BC-comb block is shorter, the resulting morphology is mainly in the large-length-scale ordering between the A-rich and C-rich domains with most of the B in the interfaces; on the other hand, when the length of the BC-comb block is long enough, we can find the hierachical structure of the same as the experiment. Therefore, along with the increase of A composition fA, the degree of polymerization in hierachical structure would increase in series as well. Finally, we manipulated interaction parameter, aAB、aAC、aBC, and found that under low aAC, we cannot observe the micro-structure of hierachical structure even if we raise aBC. This is due to the fact that the high miscibility of A and B would block the large-length-scale separation of A-coil block and BC-comb block. On the other hand, under higher aAC, the large-length-scale separation of A- coil block and BC-comb block, and the small-length scale separation of BC-domain would occur resulting from the immiscibility of A to B and A or B to C. Moreover, under very high aAC and aBC, BC-chain would stretch ever more, which then causes the large-length-scale morphology varies in the hierachical structure. By vary the value of interaction parameter, aAB、aAC、aBC, we found that hierachical structure must be formed under higher interaction parameter. To boil down, from the results we find that interaction parameter, composition, and degree of polymerization all play in indisputable role in forming hierachical structure.