Two-dimensional self-organization of gold nanoparticles on supramolecular aggregates

Alkanethiol-capped gold (Au) nanoparticles, dispersed in toluene and spin-coated on atactic polystyrene films that are themselves spin-coated on fused quartz plates, self-assemble into a characteristic two-dimensional pattern-a network of the Au-thiol nano-composite separating polystyrene 'islands' of dimensions around 200 nm. This pattern changes on varying the concentration of the nanoparticles in the coating solution, evolving into the network from isolated nanoparticle clusters, and then going over to a distribution of 'pinholes' on a surface covered by the nano-composite, resembling a partially wetted surface with near-full coverage. Study of the pristine polystyrene surface reveals a pattern of low-cohesion regions separating 'islands' of polystyrene, where the latter are known to be supramolecular aggregates. It is suggested that these regions play the role of low-resistance channels to the flow of the nano-composite during spin coating.