Tuning Molecular-Level Polymer Conformations Enables Dynamic Control over Both the Interfacial Behaviors of Ag Nanocubes and Their Assembled Metacrystals

In surface chemistry-directed nanoparticle self-assembly, it remains challenging to continuously modulate nanoparticle behavior at the oil/water interface without replacing surface functionality or particle morphology. Here, we utilize solvent-tunable molecular-level polymer conformation changes to achieve "multiple metacrystals using one nanoparticle with one chemical functionality". We use Ag nanocubes functionalized with a mixed monolayer of thiol-terminated poly(ethylene glycol) (PEG) and hexadecanethiol (C16). We continuously modulate PEG conformation from swollen to coiled states by decreasing solvent polarity, whereas C16 promotes nanocube dispersion in organic carrier solvents. Such PEG conformation changes drive Ag nanocubes to adopt tilted, standing, and planar configurations at the oil/water interface, with their interfacial positions changing from halfway across the interface to almost immersed within the oil phase. We also identify four specific polarities which enable Ag nanocubes to assemble into large-area metacrystals with linear, hexagonal, and square close-packed lattices. Our work establishes an innovative strategy to achieve robust tunability of nanoparticle interfacial behavior and unprecedented modulation of metacrystal structure.