A2-star-(B-alt-C)共聚合物結構內有結構的階級性微結構形態

Abstract

我們運用耗散粒子動力學模擬A2-star-(B-alt-C)共聚合物的相行為和分子構形分析。藉由改變作用力參數與組成，我們成功的建構A2-star-(B-alt-C)共聚合物的相圖，並發現到A塊狀接枝BC交替式塊狀的共聚合物產生二種特徵尺寸的階級性結構。首先來自於A塊狀和BC塊狀間的不相容性造成大尺寸的微結構，其微結構態與線性雙塊狀共聚合物類似。除了組成之外，我們發現B和C間的作用力參數aBC也對所形成的微結構有很大的影響。尤其是當aBC值下降，也就是B和C愈吸引在一起時，由於BC鏈段愈來愈蜷曲，因此即使當A塊狀為少量成分時，系統仍然可以經過一系列的衍變，甚至發生結構反轉的情況，也就是由BC長鏈段蜷曲形成圓柱或球。反之，隨著aBC值的增加，也就是隨著B與C間的不相容性愈來愈大，此時在BC區域中會衍生出B與C分離的小尺寸結構，因此共聚合物形成了結構內有結構的形態，隨著A組成的增加，我們觀察到的形態有 -within- 、 -within- 、 -within- 、 、 等。在探討分子構形方面，我們觀察到在固定B與C間的作用力參數下，隨著A對於B和C作用力參數的增加，系統由無序區轉變到有序區時，各臂的環動半徑值維持在一個定值，然而整體的環動半徑卻有顯著的增加，然而此時A和BC為了減少彼此的接觸，因而造成A臂和BC臂夾角增加，且A臂和A臂夾角降低。另外，我們觀察環動半徑與聚合度的關係時，隨著B對C作用力參數的增加，聚合度對環動半徑的影響將減少。

We employ the dissipative particle dynamics (DPD) to examine the microphase separation and the molecular conformation behavior of A2-star-(B-alt-C) copolymers. We find that a hierachical structure with two length scales, i.e., the so-called structure-within-structure, can be successfully induced by grafting an alternating BC block into an A block. First, similar to the linear diblock copolymers, the immiscibility parameter between A and B/C plays a dominating role for the copolymers to form an ordered microstructure at large length scale. In addition to the composition, the interaction parameter between B and C, aBC, also has a great influence on the resulting morphology geometry. In particular, as aBC decreases, i.e., when B and C components become more attractive, the BC alternating block is likely to curl more. As a consequence, even for the copolymers with the A block as a minority component, the systems can undergo a series of microphase transition into the cylinders and spheres formed by the majority BC alternating block, i.e., the so-called inverted structures. Whereas, when aBC increases, a segregation between B and C can be induced inside the B/C-rich domains. Various structure-within-structures, such as , -within- , -within- , -within- , , and are observed by increasing the A composition. In the analysis of molecular conformation, we observe that at a fixed interaction parameter between B and C, when the interaction parameter between A and B/C increases so that the systems transform from a disordered into an ordered state, the radius of gyration for each A and BC arm remains somewhat a constant; whereas the overall radius of gyration significantly increases. This manifests the fact that in order to reduce the contacts between A and BC, the angle between A and BC arms increases and the angle between A and A arms decreases.