桥连对嵌段共聚物自组装的调控

doi:10.6023/A20090438

摘要/Abstract

通过嵌段共聚物自组装形成“桥连”是制备具有优异力学性能的网络结构的有效途经, 具有重要的应用价值. 但是, 过去的研究工作很少讨论“桥连”对嵌段共聚物自组装行为本身的影响. 该研究评论主要总结了最近几年利用“桥连”对嵌段自组装行为进行调控的工作进展. 作者设计了BABCB三组分线性多嵌段共聚物, 当其自组装形成二元“介观晶体”(球、柱)结构时, 中间B嵌段连接A和C相区(嵌段聚集成的“大原子”), 自然地形成桥连; 减小中间桥连B嵌段的相对长度, 就可以增加其拉伸程度, 从而降低介观晶体的配位数; 另外, 两个末端B嵌段的相对长度可以直接调控A和C“大原子”之间的相对配位数. 基于这两个机理, 自洽场理论计算预测了各种配位数相等和不相等的二元介观晶体结构. 进一步, 将“拉伸桥连”概念拓展到AB型嵌段共聚物体系中, 并且通过多臂星型嵌段共聚物分子结构中的“组合构型熵效应”在AB型嵌段共聚物中形成高比率的桥连构型, 使传统的六角柱状结构转变为了四配位的四方柱状和三配位的石墨烯类柱状结构. 未来, 在ABC三组分嵌段共聚物体系的设计中引入拓扑结构以及使用共混等方法, 有望在介观尺度重铸大多数已知的原子/离子二元晶体结构, 甚至超越原子/离子晶体结构.

关键词: 桥连, 嵌段共聚物, 自组装, 介观晶体, 自洽场理论

To form “bridge” via the self-assembly of block copolymer provides a useful way for the fabrication of network structures of excellent mechanical properties, which is promising in applications. However, previous work has hardly paid attention to the impact of “bridge” on the self-assembly behavior of block copolymers. This account provides a review of a recent progress about the control of the self-assembly behaviors of block copolymers via the stretching degree of the bridging block. Accordingly, we have purposely designed BABCB linear multiblock copolymer. When BABCB copolymer self-assembles into binary mesocrystal structures (sphere or cylinder), the middle B-block connects a pair of A and C domains (“macromolecular atom” aggregated by blocks) naturally forming bridge. The stretching degree of the middle bridging B-block can be increased by reducing its length relative to the other two B-blocks, lowering the coordination numbers (CNs) of mesocrystal. Moreover, the asymmetry of CNs between A and C “macromolecular atoms” can be tuned by the asymmetry between the two end B-blocks. Abiding by the two principles, using self-consistent field theory (SCFT) we have predicted rich binary mesocrystals of equal and unequal CNs. Furthermore, we have extent the concept of “stretched bridge” into AB-type block copolymers. We have proposed the effect of combinatorial entropy to realize high-ratio bridging configurations in the self-assembled structures by AB-type block copolymers. By increasing the stretching degree of bridging blocks, we have successfully predicted nonclassical square array and graphene-like array of cylinders instead of the usual hexagonal array of cylinders. In future, it is hopeful to recast most of known atomic/ionic binary crystal structures or even beyond by considering topology and blending during the design of ABC-type block copolymers.

Key words: bridge, block copolymer, self-assembly, mesocrystal, self-consistent field theory

引用此文

李卫华. 桥连对嵌段共聚物自组装的调控[J]. 化学学报, 2021, 79(2): 133-138.

Weihua Li. “Bridge” Makes Differences to the Self-assembly of Block Copolymers[J]. Acta Chimica Sinica, 2021, 79(2): 133-138.

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图/表 8

图1. 拉伸桥连对ABC-型嵌段共聚物形成二元介观晶体结构的调控机理: 左图给出了ABC线性三嵌段共聚物在四方二元介观晶体中的典型链构型, 中间B嵌段形成松弛的桥连; 右图给出了BABCB五嵌段共聚物在三配位二元介观晶体中的链构型, 中间B桥连嵌段被显著拉伸.

Figure 1. Schematics demonstrating the effect of stretching bridging block on the formation of binary mesocrystals from the self-assembly of ABC-type block copolymers. The left panel presents a typical chain configuration of ABC linear triblock copolymer in the tetragonal binary mesocrystal, where the middle bridging B-block forms a large loop. The right panel shows a typical configuration of BABCB pentablock copolymer in the three-coordinated mesocrystal, where the middle bridging B-block is highly stretched.

图2. BABCB嵌段共聚物所形成的不同二元介观晶体的自由能比较以及相应的结构转变序列: χ ABN=χBCN=χACN=80, fA=fC=f和 fB1=fB3.

Figure 2. Free-energy comparison as well as the transition sequence of different mesocrystals in BABCB block copolymers with χABN=χBCN=χACN=80, fA=fC=f and fB1=fB3 (Reproduced from Ref. [15]. Copyright 2020. American Chemical Society).

图3. ABCB嵌段共聚物在χABN=χBCN=χACN 和fA=fC 条件下形成的A球(红色)比C球(蓝色)大的示意图.

Figure 3. Schematics illustrating that A-sphere (red) is larger than C-sphere (blue) in the binary mesocrystal formed by ABCB tetrablock copolymer with χ ABN=χBCN=χACN and fA=fC.

图4. χABN=χBCN=χACN=80和fA=fC=f时AB2CB3四嵌段共聚物关于f和fB2的相图以及一些典型有序结构的示意图.

Figure 4. Phase diagram with respect to fand fB2 of AB2CB3 tetrablock copolymer with χABN=χBCN=χACN=80 and fA=fC=f, as well as the schematic plots for some typical ordered structures (Reproduced from Ref. [15]. Copyright 2020. American Chemical Society).

图5. χABN=χBCN=χACN=80和fA=fC=f时B1AB2CB3嵌段共聚物关于fB2和γ=fB1/fB3的相图.

图6. 线性ABA和星型(AB)n嵌段共聚物链结构形成桥连或环构型的示意图.

Figure 6. Schematics illustrating the bridging or looping configuration formed by ABA linear and (AB)n star block copolymer architectures (Reproduced from Ref. [36]. Copyright 2020. American Chemical Society).

图7. 左边: 所设计的两个嵌段共聚物分子的结构示意图; 中间: 三个配位数不同的柱状结构中链构型的示意图, 展示了拉伸桥连效应对晶格排列的影响; 右边: 所设计的嵌段共聚物自组装形成的稳定结构的密度分布图.

Figure 7. Left: schematic plot of the architectures of two designed AB-type multiblock copolymers, M1 and M2. Center: illustrative plot of chain configurations in three typical cylindrical morphologies with different coordination numbers demonstrating the formation of bridges among neighboring domains and their impact on the domain arrangement (i.e., packing lattice). Right: density profiles of the stable morphologies self-assembled from the two block copolymers (Reproduced from Ref. [35]. Copyright 2020. American Physical Society).

图8. 在所设计的AB-型嵌段共聚物自组装结构中, 同时实现了“拉伸桥连效应”和“堆积受挫缓解效应”; 这两个效应的协同作用导致了多个新颖的低配位单元介观晶体结构的形成. 需要指出的是: B2嵌段除了可以形成桥连, 也可以形成环(loop), 也就是A1/A2和A3嵌段位于同一个A相区内, 但是该示意图没有给出这种构型.

Figure 8. “Effect of stretched bridge” and “effect of released packing frustration” are realized simultaneously in the ordered morphologies self-assembled by a purposely designed AB-type block copolymer melt, leading to the formation of a number of low-coordinated single mesocrystal structures. It is necessary to point out that B 2-block can also forming a looping configuration in addition to the bridging one, that is, A1/A2- and A3-blocks are located within the same A-domain. The looping configuration of B2-block is not shown in the schematic (Reproduced from Ref. [45]. Copyright 2020. American Chemical Society).

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