Temperature-induced self-assembly and crystallization of gold nanorods*

We report on temperature-induced and improved assembly and crystallization of gold nanorods (AuNRs) that are grafted with polye(ethylene glycol) (PEG) in electrolytic suspensions. Small angle X-ray scattering (SAXS) reveals that elevating the temperature of dispersed PEG-AuNRs suspensions in the presence of electrolytes or poly-electrolytes spontaneously induces the assembly of the AuNRs into hexagonal superlattices. Surprisingly, we find that the lattice constant of the crystalline AuNRs significantly decreases and crystal quality improves by increasing the temperature of the suspensions. Implications of the results for engineering new nanomaterials are discussed.