Tunable Sizes and Aspect Ratios of Uniform Hexagonal/Rhombic Nanosheets with a Polyethylene Core via Crystallization-Driven Self-Assembly

Block copolymers (BCPs) are well-documented to undergo self-assembly into diverse nanostructures. Uniquely, BCPs with crystallizable core-forming blocks undergo crystallization-driven self-assembly (CDSA), typically yielding one-dimensional (1D) nanowires and two-dimensional (2D) nanosheets. However, the precise control over morphologies, sizes, and aspect ratios of 2D nanosheets remains challenging. Herein, we present a one-pot “heating–cooling–aging” CDSA strategy for polyethylene-block-poly(4-tert-butoxystyrene) (PE-b-PtBOS) BCPs, which is implemented in a selective solvent of toluene over a broad concentration range of 0.025∼5.0 wt %. This strategy enables the fabrication of uniform hexagonal/rhombic nanosheets with precisely tunable sizes and aspect ratios by manipulating key parameters of the annealing temperature, the degree of polymerization for PtBOS (DPPtBOS), and concentration. Specifically, at lower DPPtBOS, spontaneous nucleation and growth enable the rapid fabrication of molecularly thin, uniform, and tunable nanosheets, whereas at higher DPPtBOS, the formation kinetics of such nanosheets slows down significantly. The nanosheet size is facilely tailorable by adjusting the annealing temperature, as this parameter directly modulates the number of crystal nuclei, while the aspect ratios of these hexagonal/rhombic nanosheets can be readily regulated by varying the concentration or DPPtBOS. Uniquely, a deliberate bidirectional morphological transition between hexagonal and rhombic nanosheets can also be achieved by modulating the DPPtBOS, concentration, and cooling rate. This work provides new insights into how experimental parameters influence the CDSA process and provides an efficient, versatile route for the controlled synthesis of 2D nanosheets.