利用分散粒子動力學探討AB2星狀高分子共聚物的相行為和分子結構分析

Abstract

我們利用分散粒子動力學模擬AB2星狀高分子共聚物的相行為和分子構形分析。藉著改變作用力參數和組成我們成功的建構了AB2星狀高分子共聚物的相圖。並且與自洽平均場 (SCMF) 理論相圖做比較，我們發現兩者在有序-無序的邊界與微結構的預測上具有非常好的一致性。然而，當B分枝的組成較小時，AB¬2星狀高分子並不容易如SCMF預期地排列形成有次序的微結構，取而代之的，它們只形成一管狀(tube-like)的相。此分散粒子動力學的結果較符合實驗上所觀察到的結果。另外，當A組成較小時，雖然如同SCMF預測的，少量的Ａ會形成球，然而我們發現有限模擬空間的大小，對其堆積的次序有著深遠的影響，我們相信這是由於系統中各種球形的堆積能量均非常相近，故系統模擬大小會控制其球形堆積。而在環動半徑Rg的分析上，隨著作用力參數的改變，當AB2由無序區進入有序區時，雖然A臂與B臂的Rg值大致不變，然而此時A成分與B成分為了減少彼此的接觸，因而造成了A臂與B臂間的夾角增大。同時造成AB2高分子共聚物的Rg上升並促使結構尺寸增大。在作用力參數固定時，A與B之間的組成越來越對稱時，由於A與B之間的互斥效應增強，造成A臂與B臂之間的夾角增大而B與B臂夾角減小。另外，藉由環動半徑和聚合度的關係，我們觀察到具分枝的B臂由於在接枝點的單位體積密度較高，造成其向外排開而較A臂更為伸展的。

We employ the dissipative particle dynamics (DPD) to simulate the microphase separation behavior of AB2 miktoarm star copolymers. The phase diagram is constructed in terms of the interaction parameters and composition, is in a near quantitative agreement with that predicted by self-consistent mean-field (SCMF) theory. However, when the composition of B is small, we observe that AB2 can not easily form the ordered microstructures as have been predicted by SCMF. Instead, they form a tube-like phase, which frequently has been observed in experiments. In addition, though the systems with smaller value of A composition form the spheres as SCMF predicted, we find that due to the finite size effects, it becomes difficult to examine the most stable packing arrays of spheres. In the analysis of radius of gyration, when the interaction parameter increases so that AB2 copolymers transform from a disordered into an ordered state, we find that the radius of gyration for each A and B arm remains somewhat a constant. However, the overall radius of gyration of AB2 significantly increases with the interaction parameter. This manifests the fact that in order to reduce the contacts between A and B, the angle between A and B arms increases and the angle between B and B arms decreases. When the interaction parameter is fixed, the radius of gyration increases with fA. By analyzing the power law , we find that the B arms are more stretchable than A arms.