Self-Assembly of A₂B Miktoarm Star Block Copolymer under Cylindrical and Spherical Confinements

Block copolymers (BCPs) are exciting materials owing to their ability to self-organize, resulting in ordered mesophases in bulk. A rich variety of interesting novel ordered phases can be obtained by subjecting the polymer to geometrical confinement. In the present study, we investigate the self-assembly behavior of A₂B miktoarm star block copolymer melt under cylindrical and spherical nanopores using self-consistent field theory (SCFT). Compared with the equivalent linear AB diblock copolymer, the A₂B miktoarm star block copolymer tends to influence the phase behavior. The structural frustration and chain conformational entropy loss lead to various ordered phases. The role of introducing an additional arm of the A-block to a linear AB diblock copolymer in phase behavior is examined for the wall selective to the majority component. Under cylindrical confinement, when the two A-arms are in the minority and the surface prefers the B-block, the region of helical phases transitions to the perforated lamella (PL₁) and concentric lamella (CL₁) phases. However, when the A-arms form the majority and prefer the surface, the helical ordering of the minority B-block is favored, and a rich array of ordered phases is obtained, such as single helix (H₁), double helices (H₂), and toroids (T). Similarly, under spherical confinement, when A-arms constitute the majority, interesting morphologies are obtained, such as double helices (H₂), four-hole nanocages (CG₄), a pair of toroids (T₂), a pair of toroids with one sphere (ST₂), and a single toroid flanked by two spheres (ST₁S). Overall, the branched chain architecture of A₂B alters the phase behavior under confinement vis-à-vis the linear AB diblock copolymer.