Basic parameters affecting nanoparticle self-assembly: An experimental approach

Understanding the basic parameters that govern the nanoparticle self-assembly process is important for high-quality monolayer formation and technological advances. A complete theory that explains nanoparticle self assembly, in the bulk and at the liquid-air interface, is lacking. In this paper, dodecanethiolated gold nanoparticles were used as a model system for studying the forces that govern self assembly. These nanoparticles are known to make compact and highly-ordered monolayers at the liquid-air interface via a mechanism that is analogous to epitaxial growth of atomic layers. Epitaxial theory was used as a starting point to study the nanoparticle self-assembly at the liquid-air interface. Experimental measurements were successfully interpreted using an epitaxy-based analysis, including flux of nanoparticles onto the liquid air-interface, decay rate of the island density, and the dependence of critical nucleus size on nanoparticle diameter. Furthermore, anomalous diffusion was observed as was a remarkable ordering of islands at the liquid-air interface. This ordering was determined to be due to a long-range repulsive force between islands.