In Situ Imaging of Active Assemblies of Nanoparticles Driven by Electric Field

Application of electric field to colloidal suspension has been shown as an efficient strategy to create dynamic materials otherwise impossible. Although numerous efforts have been devoted to the understanding and optical microscopy imaging of micron-sized colloids driven by external electric field, how nanoparticles (NPs) interact with electrodes and behave under various flow effects induced by electric field remain underexplored due to the experimental challenge to image them in-situ and the theoretical challenge to consider multiscale effects due to the small size of NPs. Here we will present our recent work on using patterned microelectrodes in a liquid-phase transmission electron microscopy chamber, to apply electric field to a NP suspension and to induce active assemblies. These assemblies are extensively dynamic and exhibit ensemble crawling motions along field gradient. Simulation of velocity flow field and electric field strength further shows how different field-induced hydrodynamic effects concur to control the active assembly. Our study can bridge the fields of active matter and colloidal NPs towards making active nanorobots and dynamic non-equilibrium assemblies.