Formation of Two-Dimensional Nanosheets with Controlled Structures via One-Step Assembly of Diblock Molecular Brushes

Two-dimensional (2D) nanosheets have drawn considerable attention due to their ultrathin planar structure and large surface area, demonstrating great potential across diverse fields. However, achieving simultaneous control over both the nanosheet geometry and size remains a significant challenge. Herein, we report a facile one-step approach for creating 2D nanosheets with controlled morphologies and sizes using PEG-b-(PtBA-g-PAzoNF) diblock molecular brushes, which consist of a poly(ethylene glycol) (PEG) block, a poly(t-butyl acrylate) (PtBA) backbone, and poly(4-((4-((nonafluoroheptyl)oxy)phenyl)diazenyl)phenyl methacrylate) (PAzoNF) side chains. The morphological transformations from symmetric hexagonal to rectangular to square nanosheets can be achieved by tuning the PAzoNF length. With long side chains, solvophobic PtBA-g-PAzoNF chains adopt a rod-like geometry and self-assemble into a columnar hexagonal structure. Upon decreasing the side-chain length, the backbone is approximately coplanar with the side chains, enabling the formation of square and rectangular nanosheets. The packing behavior of copolymer molecules was investigated through molecular dynamics simulations to verify the underlying mechanisms driving these morphological transitions. Furthermore, precise size control over these 2D nanosheets was realized by adjusting the copolymer concentration. Our study not only demonstrates the importance of the side-chain length of molecular brushes in determining their self-assembly behavior but also offers an effective strategy for designing 2D nanostructures with decent controllability.