Spatiotemporally Controlled Emergence of Nanoparticle Microvortices under Electric Field

Controlled assembly of nanoparticles (NPs) has garnered much interest over the past two decades. Beyond established techniques, new methods utilizing local short-range or large-scale long-range interactions remain to be explored to achieve diverse micro- and nanoscale structures. Here, we report the controlled emergence of vortex-pair arrays within monodispersed gold nanorods (AuNRs) by applying a direct current (dc) electric field across a pair of sawtooth electrodes. By employing in situ darkfield microscopy and particle collective analysis, we elucidate the mechanism behind the formation and stabilization of the NP vortices, attributing it to the combined effects of the electrode shape, high NP density, and high solution viscosity. We further explored the controllability of the vortex-pair arrays and obtained multiple complex vortices patterns. Our findings will facilitate the investigation of efficient and controlled dynamic assembly of NPs under external fields and help manufacture next-generation optoelectronic functional materials.