Impact of Topological Constraint on the Self-Assembly Behavior of AB-Type Block Copolymers

Chain topology has an important impact on the phase behaviors of block copolymers, even for two-component AB-type ones. To demonstrate this impact, a special type of AB-type copolymers is purposely devised by tethering an additional A block onto the B-block of AB diblock copolymer. With the tethering position at the junction point of AB, the copolymer becomes A₂B miktoarm star while it becomes ABA linear triblock with the tethering position at the end of B-block. The phase diagrams of the AB-type copolymers with various grafting positions are constructed using the self-consistent field theory. Surprisingly, the perforated lamellar (PL) phase with perforated A-layer becomes stable and completely replaces gyroid at relatively strong segregation for the AB-type copolymer with a proper tethering position, which is in obvious contrast to a tiny stability channel in A₂B or no stability region in ABA. It is elucidated that PL is stabilized by the local segregation of the two divided B-blocks, accommodating to the distinct interfaces with highly different curvatures.