Zheng Lingfei, Wu Jianqi, Wang Zheng, Yin Yuhua, Jiang Run, Li Baohui
School of Physics, Key Laboratory of Functional Polymer Materials of Ministry of Education, Nankai University, and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), 300071, Tianjin, China.
Kavli Institute for Theoretical Physics China, CAS, 100190, Beijing, China.
Eur Phys J E Soft Matter. 2016 Jul;39(7):75. doi: 10.1140/epje/i2016-16075-8. Epub 2016 Jul 28.
The phase behavior of symmetric ABC triple-hydrophilic triblock copolymers in concentrated aqueous solutions is investigated using a simulated annealing technique. Two typical cases, in which the hydrophilicity of the middle B-block is either stronger or weaker than that of the end A- and C-blocks, are studied. In these two cases, a variety of phase diagrams are constructed as a function of the volume fraction of the B-block and the copolymer concentration ([Formula: see text] for both non-frustrated and frustrated copolymers. Structures, such as two-color alternatingly packed cylinders or gyroid, and lamellae-in-lamellae etc. that do not occur in the melt system, are obtained in solutions. Rich phase transition sequences, especially re-entrant phase transitions involving complex continuous networks of alternating gyroid and alternating diamond are observed for a given copolymer with decreasing [Formula: see text] . The difference in hydrophilicity among different blocks can result in inhomogeneous distribution of solvent molecules in the morphology, and with the decrease of [Formula: see text] , the distribution of solvent molecules presents a non-monotonic variation. This results in a non-monotonic variation of the effective volume fraction of each domain with the decrease of [Formula: see text] , which induces the re-entrant phase transitions. The presence of a good solvent for all the blocks can cause changes in the effective segregation strengths between different blocks and also in chain conformations, hence can alter the bulk phases and results in the occurrence of new structures and phase transitions. Especially, structures having A-C interfaces or A-C mixed domains can be obtained even in the non-frustrated copolymer systems, and structures obtained in the frustrated systems may be similar to those obtained in the non-frustrated systems. The window of the alternating gyroid structures may occupy a large part of the phase diagram for non-frustrated copolymers with stronger B-hydrophilicity. This behavior can be used to tune the self-assembled structures of block copolymers.
采用模拟退火技术研究了对称ABC三亲水性三嵌段共聚物在浓水溶液中的相行为。研究了两种典型情况，即中间B嵌段的亲水性强于或弱于末端A和C嵌段的亲水性。在这两种情况下，构建了各种相图，其作为B嵌段的体积分数和共聚物浓度（对于非受挫和受挫共聚物均为[公式：见正文]）的函数。在溶液中获得了熔体体系中不存在的结构，如双色交替堆积圆柱或螺旋状结构以及片层中片层等。对于给定的共聚物，随着[公式：见正文]的降低，观察到丰富的相变序列，特别是涉及交替螺旋状和交替菱形复杂连续网络的再入相变。不同嵌段之间亲水性的差异会导致溶剂分子在形态上的不均匀分布，并且随着[公式：见正文]的降低，溶剂分子的分布呈现非单调变化。这导致每个区域的有效体积分数随着[公式：见正文] 的降低而非单调变化，从而引发再入相变。对所有嵌段均为良溶剂的存在会导致不同嵌段之间有效分离强度以及链构象的变化，因此会改变本体相并导致新结构和相变的出现。特别是，即使在非受挫共聚物体系中也可以获得具有A - C界面或A - C混合区域的结构，并且在受挫体系中获得的结构可能与在非受挫体系中获得的结构相似。对于具有较强B亲水性的非受挫共聚物，交替螺旋状结构的窗口可能占据相图的很大一部分。这种行为可用于调节嵌段共聚物的自组装结构。
