Tailoring Assembly Pathways of Gold Nanorods via Controlled Electrostatic Screening

Precise control over the self-assembly pathways of anisotropic nanoparticles into supercrystals is essential for constructing functional nanodevices and metamaterials with tailored superstructures. However, the crystallization of nanoparticle systems via the conventional electrostatic screening method usually leads to uncontrolled aggregation, thereby limiting the observation of superstructural phase behaviors. Herein, we achieve superstructural phase transitions of gold nanorods (GNRs) from 2D parallel superlattices to 3D parallel superlattices and 2D vertical superlattices via fine electrostatic screening modulation, using hydrochloric acid (HCl) as a unique volatile electrolyte in a bulk solvent evaporation process. Remarkably, two exotic local tetragonal packing (TP) modes of GNRs are realized, where the TP-I mode arises from the sequential sedimentation of nanorods onto pre-deposited colloidal clusters, and the TP-II mode originates from linear dislocations induced by interfacial compression. Both self-assembly mechanisms are mediated by colloidal clusters, in contrast to the normal crystallization pathways based on direct monomer addition. This work highlights a feasible strategy for tailoring superstructural phase transitions of anisotropic nanoparticles, and provides a versatile route for engineering assemblies and metamaterials with desired architectures.