Self-Assembly of Asymmetric Diblock Copolymers under the Spherical Confinement

Abstract

The self-assembly of asymmetric AB diblock copolymer melts under the spherical confinement with surface preference to the minority A-block has been investigated using the pseudospectral method of self-consistent field theory coupled with the masking technique. A phase diagram with respect to the volume fraction and the radius of the spherical cavity is constructed, mainly consisting of different spherical and cylindrical structures. In contrast to the bulk disorder/sphere/cylinder/gyroid transitions, the spherical confinement shifts the corresponding transitions toward small volume fraction. For the spherical structures, the number of spherical domains increases with the radius of the cavity, but it changes discontinuously. In general, the higher the symmetry of the sphere arrangement, the larger the stability region of the spherical structure. In addition, a number of interesting cylindrical structures are predicted, such as truncated single-helix, double-toroid, and three-/four-/six-hole cages. Compared with the spherical structures, the transitions between the different cylindrical structures are more difficult to understand because the spherical confinement impacts not only the length of the cylindrical domain but also its orientation. Our work provides an insight into the influence of the spherical confinement on the self-assembly of block copolymers, especially on the arrangement of soft spherical domains.