Cylindrical phase of diblock copolymers confined in thin films. A real-space self-consistent field theory study

We have used real-space self-consistent field theory to search possible morphology of an asymmetric AB diblock copolymer thin film confined between two homogeneous hard walls. The volume fraction of the A block is fixed to be f=0.3, as expected, a cylindrical phase is stable without confinement (in the bulk). Our simulation reveals that under confinement, in addition to parallel and perpendicular cylinders, other phases, such as flat lamellae, perforated lamellae, undulated cylinders and undulated lamellae, are also stable due to the block–substrate interactions. Three new structures, i.e. undulated lamellae, undulated cylinders and parallel cylinders with non-integer period, are observed to be stable with suitable film thickness and block–substrate interaction. By systematically varying the film thickness and the interaction parameters between the two blocks, phase diagrams are constructed for typical block–substrate interactions. We compare the phase diagrams for weak and strong substrate preference and discuss the effects of confinement and substrate preference on the stability of various structures.