Tunable Two-Dimensional Self-Assembly of Ag Nanocubes with Binary Ligands—A Computational and Experimental Study

Interfacial assembly of shaped Ag nanoparticles (NPs) into two-dimensional structures provides a promising approach for generating nanomaterials with novel plasmonic properties. However, assembling such NPs at interfaces into 2D tunable non-close packed arrangements is challenging. In this talk, we propose the use of binary (hydrophilic and hydrophobic) ligands to manipulate the interactions between shaped Ag NPs and thereby to achieve the tunability of their assembly at an air-water interface. We demonstrate through both molecular dynamics simulations and experiments that the interactions between Ag nanocubes grafted with mixed hydrophilic/hydrophobic (PEG thiol/hexadecanethiol) ligands can be manipulated and their assembly can be controlled by changing the length and stoichiometry of the two ligands. We systematically explore the structural phases assembled from such grafted nanocubes by tuning the overall surface grafting densities and the length and number ratios of the two ligands, which reveals interesting phases of assembly. A fascinating finding of them is the formation of a novel checkerboard pattern of Ag nanocubes due to the interplay between the two ligands. We also show that Ag nanocubes at the air-water interface can experience multi-phase transitions in response to Langmuir-Blodgett compression. In addition, we study the orientational behavior of such nanocubes at the interface and highlight its importance on their assembly.