Bidispersity-Induced Novel Self-Assembly Behaviors in Homopolymer-Tethered AB Diblock Copolymers

In the previous work (Macromolecules 2018, 51, 1529–1538), self-consistent field theory (SCFT) predicted a considerable stability region of the perforated lamellar (PL) phase in an ABAT block copolymer melt. However, this work overlooked some candidate phases, especially the O70 network phase in the intermediate or strong segregation regime, as well as the unusual single-gyroid (SG) network phase, which has recently been identified as stable in some AB-type multiblock copolymer melts. Accordingly, in the current work, we re-examine the self-assembly behavior of the A1B(A2)T block copolymer using SCFT by including a more complete library of candidate phases. In addition to the architectural parameter τB characterizing the length ratio of the middle B1-block to the total B-blocks, we also consider the length ratio τA of the tail A1-block to the total A-blocks. SCFT calculations predict a stable O70 phase, an SG phase, a square array of cylinders (C4) with a low coordination number (CN) of 4, and a simple cubic (SC) spherical phase with a low CN of 6. It is revealed that both τA and τB play important roles in determining the relative stability of these different network phases. Furthermore, by analyzing the distributions of different blocks, we have also attempted to explain the relative stability between the hexagonally close-packed (HCP) and face-centered cubic (FCC) phases, both of which exhibit considerable stability regions in the phase diagrams of the A1B(A2)T copolymer. Our work provides new insights into the stabilization mechanisms of these interesting phases including the O70, SG, and HCP/FCC phases.