Gold nanoparticle shape dependence of colloidal stability domains

Controlling the spatial arrangement of plasmonic nanoparticles is of particular interest to utilize inter-particle plasmonic coupling, which allows changing their optical properties. For bottom-up approaches, colloidal nanoparticles are interesting building blocks to generate more complex structures via controlled self-assembly using the destabilization of colloidal particles. For plasmonic noble metal nanoparticles, cationic surfactants, such as CTAB, are widely used in synthesis, both as shaping and stabilizing agents. In such a context, understanding and predicting the colloidal stability of a system solely composed of AuNPs and CTAB is fundamentally crucial. Here, we tried to rationalize the particle behavior by reporting the stability diagrams of colloidal gold nanostructures taking into account parameters such as the size, shape, and CTAB/AuNP concentration. We found that the overall stability was dependent on the shape of the nanoparticles, with the presence of sharp tips being the source of instability. For all morphologies evaluated here, a metastable area was systematically observed, in which the system aggregated in a controlled way while maintaining the colloidal stability. Combining different strategies with the help of transmission electron microscopy, the behavior of the system in the different zones of the diagrams was addressed. Finally, by controlling the experimental conditions with the previously obtained diagrams, we were able to obtain linear structures with a rather good control over the number of particles participating in the assembly while maintaining good colloidal stability.

Automated summary

This study aimed to understand and predict the colloidal stability of colloidal gold nanostructures composed of AuNPs and CTAB. It was found that the shape of nanoparticles had an impact on the overall stability, with the presence of sharp tips being the source of instability. A metastable area was systematically observed in the stability diagrams, where the system aggregated in a controlled way while maintaining colloidal stability. By combining strategies and using transmission electron microscopy, the behavior of the system in different zones of the diagrams was investigated. Linear structures with good control over the number of particles participating in the assembly and good colloidal stability were obtained by controlling the experimental conditions with the previously obtained diagrams.