Entropy-Driven Assembly of Nanoparticles within Emulsion-Evaporative Block Copolymer Particles: Crusted, Seeded, and Alternate-Layered Onions

Hybrid organic/inorganic systems with modulated nanostructures and well-defined morphologies are of great importance to develop novel nanomaterials with tailored functionalities. Herein, we report the tunable assemblies of polystyrene-grafted Au nanoparticles (Au@PS NPs) within onion-like particles of polystyrene-b-poly­(4-vinylpyridine) (PS-b-P4VP), controlled by the molecular weight (M_n) of PS ligands. Coassembly of Au@PS and PS-b-P4VP through solvent-evaporative emulsions exhibits dramatic morphological changes in the NP assemblies depending on the M_n of PS ligands: (1) addition of low M_n (1.8 kg mol^–1) Au@PS creates crusted onion-like hybrid particles with well-ordered hexagonal NP superlattices covering their surface; (2) in contrast, high M_n (6.4 kg mol^–1) Au@PS segregate at PS domains of the block copolymer particles. Interestingly, these NPs form a hexagonal packing structure at the center of the PS domains, producing concentric lamellar particles with hierarchically stacked Au@PS in an alternate-layered onion-like structure. Finally, cryogenic electron microscopy analysis is conducted to probe the entropy-driven mechanism of the formation of these hybrid particles. These initial demonstrations of multicomponent hybrid particles with targeted spatial alignments offer new strategies to design complex nanomaterials with tailorable properties for potential technological applications.