桥连对嵌段共聚物自组装的调控

“Bridge” Makes Differences to the Self-assembly of Block Copolymers

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径,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.

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.