Gavrilov Alexey A, Shupanov Ruslan M, Chertovich Alexander V
Physics Department, Lomonosov Moscow State University, 119991 Moscow, Russia.
Semenov Federal Research Center for Chemical Physics, 119991 Moscow, Russia.
Polymers (Basel). 2020 Nov 5;12(11):2599. doi: 10.3390/polym12112599.
In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA); a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block increases (the length of the solvophilic block was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium; the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower / values; a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer; however, the positions of the transition lines for PISA are slightly shifted towards higher / values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.
在这项工作中，我们构建了理想二嵌段共聚物溶液的详细相图，并将其与聚合诱导自组装（PISA）过程中获得的相图进行了比较；研究了广泛的聚合物浓度以及链组成。随着疏溶剂嵌段长度的增加（亲溶剂嵌段长度固定），会发生从球形胶束到圆柱状，再到囊泡（片层）的转变。我们观察到在球形和圆柱状形态之间存在一个相当宽的转变区域，其中系统包含球体和短圆柱的混合物，它们似乎处于动态平衡；发现圆柱状和囊泡之间的转变相当尖锐。接下来，随着系统中聚合物浓度的增加，球体和圆柱状之间的转变区域向更低的/值移动；对于圆柱状和囊泡之间的转变也观察到了类似但幅度较小的移动。这种行为归因于在较高聚合物体积浓度下胶束之间接触数目的增加。我们还发现，对于小聚合物体积浓度，圆柱状胶束稳定区域的宽度与分析理论的预测在定量上吻合良好。所获得的PISA相图与预合成二嵌段共聚物的情况相似；然而，与预合成二嵌段共聚物相比，PISA转变线的位置向更高的/值略有偏移，这在圆柱状到囊泡转变的情况下更为明显。我们认为这种行为的原因是形成核的嵌段的多分散性：分别位于胶束界面和中心的短嵌段和长嵌段的存在有助于减少由于不溶性嵌段拉伸导致的熵损失，这导致更弯曲胶束的稳定性增加。
