Phase behavior of disk-coil block copolymers under cylindrical confinement: Curvature-induced structural frustrations

We explore the self-assembly of disk-coil block copolymers (BCPs) confined within a cylinder using molecular dynamics simulations. We obtained concentric lamellar structures with a different number of alternating disk-rich and coil-rich bilayers as a function of the cylinder diameter and coil length. Our study focuses on the curvature-induced structural behavior in the disk-rich domain after self-assembly, investigated by local density distribution P(r) and orientational distribution G(r, θ). In the inner layers of the cylinder-confined system, both P(r) and G(r, θ) show characteristic asymmetry within a bilayer, directly contrasted to its bulk and slab-confined counterparts. We successfully attribute the curvature-induced structural behavior of disks to (1) packing frustration of disks, and (2) asymmetric stretching of coils to regions with different curvatures of a bilayer. Our results are important to understand the self-assembly of BCPs containing rigid motif in confinement, such as the self-assembly of bacteriochlorophyll confined by lipid layer to form a chlorosome, the photosynthetic antennae complex found in nature.