Anomalous solubility behavior of mixed monolayer protected metal nanoparticles

Abstract

The solubility of mixed monolayer protected gold nanoparticles was studied. Monolayer protected metal nanoparticles are attractive materials because of the optical and electronic properties of their metal cores and because of the surface properties of their ligand coating. Recently, it was discovered that a mixture of ligands phase separate into ordered domains of single nanometer or subnanometer width on the surface of metal nanoparticles. The morphology and length of the ligand domains (which take the form of ripples on the particle surface) has given these nanoparticles novel properties. Because monolayer protected nanoparticles can be dissolved and dried many times, they can be handled and processed in ways not available to other nanomaterials. Understanding the solubility of mixed monolayer protected metal nanoparticles could help in implementing their unique new properties. This study demonstrates that the solubility of these particles in organic solvents cannot be explained only in terms of the composition of the ligand shell. Instead, solubility is also closely linked to morphology of the ligand shell via relationships between the size of the solvent molecule and the size of the features in the morphology.