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

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.