Emergence and Stability of Exotic “Binary” HCP-Type Spherical Phase in Binary AB/AB Blends
Fengmei Zhao, Qingshu Dong, Qingyun Li, Meijiao Liu, Weihua Li
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 ABn copolymer as n approaches infinity. More surprisingly, a novel “binary” HCP-type spherical structure (HCPb) is discovered when the two AB diblocks differ greatly in both volume fraction and polymerization degree. The HCPb 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.