Self-Assembly of Ionic Au Nanoparticles into Facet-Controllable Supercrystals

As one of the fundamental interactions in nature, electrostatic interaction plays an important role in assembling ionic molecules into various functional units in living system, which facilitates many applications such as molecular recognition and regulation of catalytic reactions. While the self-assembly of nanocrystals into well-ordered three dimensional structures can lead to novel collective properties, in addition to the unique properties of individual nanocrystals. Here we employ electrostatic interactions with other short-range interactions like hydrogen bond, try to study the self-assembly behaviors of these ion-like nanoparticles, which would also provide great opportunities to obtain interesting superstructures in water.

My work starts with designing simple positive and negative Au nanoparticles with well-defined quaternary ammonium and carboxylate ligand shells as model particles. By employing titration reactions between these ionic nanoparticles, we will show an interesting order-determined self-assembly behavior, which can be well explained with different coordination numbers originated from pH-depended hydrogen bonding. We will also give some examples on trying to explore new superstructures based on these ionic nanoparticles. To avoid the strong attractive forces between positive and negative nanoparticles, we develop a salt-mediated method to reduce the attractive force between ionic nanoparticles. Then by the decomposition of the salt, these ionic nanoparticles are destabilized in a controllable manner which finally leads to a variety of facet-specific supercrystals.