Ordered Networks of Gold Nanoparticles Crosslinked by Dithiol-Oligomers

Controlled aggregation of nanoparticles into superlattices is a grand challenge in material science, where ligand based self-assembly is the dominant route. Here, the self-assembly of gold nanoparticles (AuNPs) that are crosslinked by water soluble oligo-(ethylene glycol)-dithiol (oEG-dithiol) is reported and their 3D structure by small angle X-ray scattering is determined. Surprisingly, a narrow region is found in the parameter space of dithiol linker-length and nanoparticle size for which the crosslinked networks form short-ranged FCC crystals. Using geometrical considerations and numerical simulations, the stability of the formed lattices is evaluated as a function of dithiol length and the number of connected nearest-neighbors, and a phase diagram of superlattice formation is provided. Identifying the narrow parameter space that allows crystallization facilitates focused exploration of linker chemical composition and medium conditions such as thermal annealing, pH, and added solutes that may lead to superior and more robust crystals.