Emergence and Stability of Exotic “Binary” HCP-Type Spherical Phase in Binary AB/AB Blends

Abstract

Blending two different AB diblock copolymers provides a simple way to enlarge the volume fraction of spherical domains and thus to stabilize various Frank−Kasper spherical phases. What are the limits of the volume fraction and the difference between the two AB diblock copolymers that can be accommodated into a spherical phase? To answer this question, we extend the phase diagram of the binary AB/AB blends by pushing the bidispersity to high degrees based on the calculation of the self-consistent field theory, focusing on the formation of the spherical phases. We find that the average volume fraction of A-blocks for Frank−Kasper A-spherical phases reaches 0.4, which is even larger than the limit obtained by the miktoarm AB n copolymer as n approaches infinity. More surprisingly, a novel "binary" HCP-type spherical structure (HCP b ) is discovered when the two AB diblocks differ greatly in both volume fraction and polymerization degree. The HCP b phase contains large spheres of the core−shell structure co-assembled by two AB diblocks and small spheres formed by nearly pure short AB diblocks. Our work not only deepens the understanding of the self-assembly of AB/AB blends but also may promote relevant experimental studies.

Phase Behavior of Binary Blends of Diblock Copolymers: Progress and Opportunities

“…The HCP b phase is stable when the reduced chain stretching free energy of the longer copolymers outweighs the extra interfacial free energy induced by forming small spheres to fill the interstitial voids. The discovery of the HCP b phase unveiled another type of chain arrangement in binary A 1 B 1 /A 2 B 2 blends, consisting of copolymers with a great difference in degrees of polymerization, i.e., forming larger and smaller spheres and packing in a way that conforms to Horsfield close packing model. , It would be interesting to confirm the formation of this novel HCP b phase in experiments.…”

“…Following the previous study by Liu et al on the A 1 B 1 /A 2 B 2 mixtures, , Zhao et al extended the SCFT calculations to investigate the phase behavior when the two diblock copolymers have a much larger difference in their lengths, i.e., γ = N 2 / N 1 > 2. It is very interesting that their theoretical study predicted that a novel “binary” HCP (HCP b ) phase, composed of larger and smaller spheres with vastly different volumes, becomes stable when γ ≳ 2.6.…”

“…A schematic of the novel HCP b phase is also included, along with the phase diagram. Reprinted with permission from ref , Copyright 2022 American Chemical Society.…”

The impact of intramolecular polydispersity on the self-assembly of ABn miktoarm star copolymers

“…At the same time, large polydispersity can induce macrophase separation that may suppress the formation of complex phases. 42,65,66 In striking contrast, the intramolecular polydispersity does not induce macrophase separation. The common feature of intermolecular and intramolecular polydispersities is that both of them can release the packing frustration.…”

Asymmetric Binary Spherical Phases Self-Assembled by Mixing AB Diblock/ABC Triblock Copolymers

“…Otherwise, the blend tends to occur macroscopic phase separation, resulting in the coexistence of two ordered phases. Previous works reveal that two different AB diblock copolymers with largely different values of γ can become compatible by judiciously choosing their compositions. − More specifically, the stable region of the spherical phase with respect to the volume fraction can be significantly expanded in the AB/AB blend with optimized parameters, leading to the formation of complex Frank–Kasper phases. ,,, …”