Ordering Dynamics of Cylinder-Forming AB Diblock Copolymers under Triangular Confinement

Abstract

Previous studies have shown that the thermodynamic equilibrium structure of cylinder-forming AB diblock copolymer thin films under the lateral confinement of regular triangles with neutral top and bottom surfaces is always perfectly hexagonally arranged perpendicular cylinders. However, for practical applications, a more critical question is whether these perfect hexagonal patterns can be kinetically realized within a reasonably short annealing time. In this work, we employ coarse-grained dissipative particle dynamics simulations to investigate the self-assembly of cylinder-forming diblock copolymers under regular triangular confinement, aiming to determine the size window for achieving perfect hexagonal cylindrical patterns within a given short simulation time. Our results show that when the side length of the triangle, L, is small, with no more than 7 cylinders along each side, perfect hexagonal patterns are always obtained. As L increases such that the number of cylinders per side ranges from 8 to 15, the L window for each hexagonal pattern remains wide, and defects only emerge near the boundaries between two adjacent windows, primarily due to the formation of different numbers of cylinders along different triangular sides. For even larger L, with up to 19 cylinders per side, a notable L window for perfect hexagonal patterns still persists. By mapping the single-chain diffusion time between simulation and experiment, the simulation times chosen in our work are estimated to correspond to very short annealing times in experiments. Our work demonstrates that triangular confinement can rapidly direct cylinder-forming block copolymers to self-assemble into perfectly hexagonally arranged perpendicular cylinders over a wide range of L, providing a simple strategy for the fabrication of large-scale ordered hexagonal patterns.