Effect of ratio of hydrophilic and hydrophobic ligand length on the adsorption behaviors of amphiphilic gold nanoparticles at the liquid-liquid interface

Abstract

Amphiphilic gold nanoparticles (AuNPs) covered with hydrophobic and hydrophilic ligands assemble at the interface between hexane and water into monolayer structures, forming microdroplets that are covered with amphiphilic AuNPs. Here, we focused on the effect of the ratio of hydrophilic to hydrophobic ligand lengths on the assembly of amphiphilic AuNPs at the interface surface. By controlling the ratio, the extent of amphiphilic AuNPs migrating to the interface was examined. The amphiphilic AuNPs tended to migrate to the interface with an increase in the length of hydrophobic ligands. More importantly, diverse adsorption isotherm models were applied to the systems to examine the adsorption behavior of amphiphilic AuNPs at the interface. Adsorption parameters such as equilibrium constant and maximum uptake depending on the ratio of ligand length were obtained from data fitting, and they had high values with an increase in the hydrophobic ligand length. These results suggest that the adsorption behavior of amphiphilic AuNPs at the interface can be controlled by adjusting the ligand length ratio. Furthermore, the closest distance between amphiphilic AuNPs at the interface by using the obtained maximum uptake values was estimated, and it also was confirmed by the small-angle X-ray scattering (SAXS) technique.