Tuning Helical Structures via Designed Block Copolymer Systems

Block copolymers confined in nanopores provide unique achiral systems for the formation of helical structures. With AB diblock copolymers, stable single and double helical structures are observed. Aiming to obtain more different helical structures, we replace AB diblock copolymer with linear ABC triblock copolymers. We speculate that a core-shell superstructure is formed within the nanopore, which is composed of a C-core cylinder wrapped by B-helices within the A-shell. A number of helical structures with strands ranging from 1 to 5 are predicted by self-consistent field theory (SCFT), and in general, the number of strands decreases as the volume fraction of C-block f_C increases in a given nanopore. More surprisingly, the variation of helical strand in the confined system is in an opposite trend to that in the bulk, which is mainly resulted by the constraint of the cylindrical confinement on the change of the curvature between the outer A-layer and the inner B/C-superdomain. Furthermore, adding C homopolymers to ABC triblock copolymers, the helical structures with more strands are predicted. Our work demonstrates a facile way to fabricate different helical superstructures.