Controlled chainlike agglomeration of charged gold nanoparticles via a deliberate interaction balance

Chain-like agglomeration (one-dimensional self-assembly) of aqueous gold nanoparticles (NPs) has been experimentally and theoretically studied. It is demonstrated that the chain growth of aqueous gold NPs is mainly triggered by the anisotropic dipolar interaction due to the Au-S bonding originating from the thiolligand capping, plus van der Waals interaction. This anisotropic self-assembly can be endorsed by the isotropic electrostatic repulsion between the gold NPs, which can be finely tuned by the dielectric constant of the surrounding media of the NPs that is dependent on the volume ratio of water to a polar organic solvent. Adding more thiol-ligands or NaCl brings a similar effect of increasing the ionic strength of the NP suspensions, thus lowering the electrostatic repulsion between and, at a certain range, accelerating chain-like agglomeration of the NPs. The use of various thiol-ligands with different terminal groups allow involvement of other interactions, including hydrophobic interaction and hydrogen bonding, between charged gold NPs, which gives rise to a faster kinetic of chain-like agglomeration.