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

Abstract

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.

Self-Assembly of Asymmetric Diblock Copolymers under the Spherical Confinement

“…The self-assembly of block copolymers has attracted tremendous attention of scientists due to the potential applications in a wide range of fields, for example, lithographic templates for nanowires, photonic crystals, or high-density magnetic storage media. − These applications mainly make use of the ability of block copolymers to spontaneously self-assemble into periodic nanostructures. , The AB diblock copolymer as the simplest block copolymer, which consists of two chemically incompatible blocks linked by covalent bonds, can form a variety of ordered phases, including a body-centered cubic (BCC) lattice of spheres, hexagonally coordinated cylinders, double gyroid, and lamellae. − In general, the self-assembly of block copolymers is dictated by the competition between the interfacial and entropic contributions of free energy . The competition of the two contributions can be largely controlled by tailoring the chain architectures of multiblock copolymers, providing an unparalleled opportunity for the formation of novel ordered structures. − On the other hand, some external conditions can be introduced to alter the competition and thus to make block copolymers self-assemble into different structures from their bulk phases.…”

Control the Self‐assembly of Block Copolymers by Tailoring the Packing Frustration

“…Besides the effect of tailored packing frustration, the effects of spontaneous curvature and stretched bridging block also play important roles on the formation of ordered nanostructures from the self‐assembly of block copolymers. [ 16,41‐42 ] Accordingly, Li and coworkers have proposed valid strategies of designing the architectures of block copolymers to realize the effects of spontaneous curvature and stretched bridging block and thus to control the self‐assembly of block copolymers for achieving novel nanostructures. [ 15,32,42‐43 ] They have also attempted to design block copolymers to realize these different effects simultaneously, the synergistic effect of which leads to a lot of interesting and even unusual self‐assembly behaviors.…”

“…[ 16,41‐42 ] Accordingly, Li and coworkers have proposed valid strategies of designing the architectures of block copolymers to realize the effects of spontaneous curvature and stretched bridging block and thus to control the self‐assembly of block copolymers for achieving novel nanostructures. [ 15,32,42‐43 ] They have also attempted to design block copolymers to realize these different effects simultaneously, the synergistic effect of which leads to a lot of interesting and even unusual self‐assembly behaviors. [ 26,44 ] For example, as mentioned previously, they have obtained the graphene‐like array of alternating cylinders with CN = 3 in the self‐assembly of purposely designed AB(B T )C block copolymers with a synergistic effect of tailored packing frustration and stretched bridging block.…”

Largely Tunable Morphologies Self-Assembled by A(AB)n Miktoarm Star Copolymer in Solutions

“…By contrast, the strategies of regulating nanostructures by designing the architecture of AB-type copolymer in bulk are relatively definite, − which might provide a helpful guide for controlling the self-assembly behaviors in solution. Based on the SCFT calculations, Li and co-workers have proposed a series of guiding principles to tailor molecular topology via realizing the effects of spontaneous curvature, stretched bridging block, released packing frustration and local segregation individually or synergistically. ,,− Among these strategies, tuning the effect of spontaneous curvature provides a direct and effective pathway to controlling self-assembly behavior. , The spontaneous curvature is an intrinsic property of the block copolymer originating from compositional or architectural asymmetry, indicating the tendency or preference of the interfacial curvature when self-assembled structures are formed. − For instance, a composition-asymmetric AB diblock copolymer with the volume fraction of A-block f A < 0.5 tends to form structures with interfacial curvature toward the A-domain in bulk. Introducing topological asymmetry is a more effective route to increase spontaneous curvature, which leads to an asymmetric phase diagram with an expanded spherical phase region. − As a consequence, the enlarged volume fraction of spherical domains drives them to pack into complex unconventional crystal lattices.…”