Cluster Size Analysis of Two-Dimensional Order in Colloidal Gold Nanoparticle Arrays

A protocol for cluster size distribution analysis was developed in order to parametrize local two-dimensional (2D) order in a quantitative manner, using mean cluster sizes and fractional hcp cluster formation (f_hcp). Cluster size analysis was performed on 2D arrays of Au nanoparticles encapsulated in resorcinarene tetrathiol, which were organized into close-packed films at aqueous interfaces. The degree of monolayer formation and 2D order within the self-assembled nanoparticle arrays was observed to be strongly dependent on the amount and type of electrolyte (chloride and/or citrate) adsorbed on the nanoparticle surface, prior to encapsulation and extraction to the solvent interface. Increasing the concentration of adsorbed electrolyte could promote monoparticulate film formation but had a variable effect on local 2D order.