Emergence of Multi-strand Helices from the Self-Assembly of AB- Type Multiblock Copolymer under Cylindrical Confinement

The self-assembly of block copolymers under the confinement of nanopores provides a facile way for the formation of helical nanostructures. However, these helical structures usually have a small number of helical strands, such as single or double helix. In this work, we study the self-assembly of a (BT)AB(AT)-multiblock copolymer melt under the confinement of nanopores using self consistent field theory, aiming to explore multi-strand helical nanostructures. Different helical structures with the number of strands ranging from 1 to 6 have been successfully predicted by tailoring the architecture of this copolymer. We find that the helical structures with an increasing number of strands are formed, accompanied by the bulk phase transition from the classical high-coordinated hexagonal cylinder phase to the low-coordinated cylinder phase (e.g., square lattice) that is controlled by the copolymer architecture. Our results further reveal that these multi-strand helical structures are mainly stabilized by the unique ability of the specific architecture to relieve the packing frustration of the majority blocks. Therefore, the formation of multi-strand helical structures is robust for AB-type block copolymers whose bulk cylinder phases are low coordinated.

Automated summary

In this study, the self-assembly of a multiblock copolymer melt was investigated under the confinement of nanopores. Different multi-strand helical structures were successfully predicted by tailoring the copolymer architecture. The results showed that these helical structures are mainly stabilized by the unique ability of the specific architecture to relieve the packing frustration of the majority blocks.