Tunable formation of two-dimensional nanostructures and complex crystals via lead(II) bromide complexation and...

We report the formation of two-dimensional (2D) hairy nanostructures-irregular nanosheets and polygonal nanoplates-via inclusion crystallization between polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and lead(II) bromide (PbBr₂) in 1,3,5-trimethylbenzene (TMB). The irregular nanosheets are composed of orthorhombic complex crystals with Cmca symmetry and the polygonal nanoplates are composed of hexagonal complex crystals with P6mm symmetry. Systematic variation of the PS-b-PEO/PbBr₂ ratio reveals that both components critically influence the morphology and crystallinity of the resulting structures. At a fixed PbBr₂ concentration (10 mg mL^-1), increasing PS-b-PEO content initially promotes the formation of both nanosheets and nanoplates, but at higher concentrations favors polygonal nanoplates while suppressing irregular nanosheets. Conversely, at a fixed PS-b-PEO level (1 mg mL^-1), increasing PbBr₂ enhances complexation as reflected in UV-vis absorbance spectra, but the formation of complex crystals behaves differently due to polymer saturation and dilution effects. WAXD analysis reveals that inclusion crystallization occurs most efficiently at moderate PbBr₂ loading (0.1 and 1 mg mL^-1) to simultaneously form a high crystallinity of orthorhombic and hexagonal complex crystals. However, excess PbBr₂ leads to the formation of crystalline PbBr₂ domains and results in the formation of irregular nanosheets with low crystallinity without forming polygonal nanoplates. These findings demonstrate that the polymer-to-salt ratio governs the polymorphism behavior and efficiency of inclusion crystallization, and further indicate that PbBr₂ complexation and crystalline ordering are decoupled processes. This work offers mechanistic insights into polymer-salt ratio-controlled inclusion crystallization, providing a tunable approach for constructing anisotropic hairy nanostructures.