Structural transitions in nanoparticle assemblies governed by competing nanoscale forces.

Assembly of nanoscale materials from nanoparticle (NP) building blocks relies on our understanding of multiple nanoscale forces acting between NPs. These forces may compete with each other and yield distinct stimuli-responsive self-assembled nanostructures. Here, we report structural transitions between linear chains and globular assemblies of charged, polymer-stabilized gold NPs, which are governed by the competition of repulsive electrostatic forces and attractive poor solvency/hydrophobic forces. We propose a simple quantitative model and show that these transitions can be controlled by the quality of solvent, addition of a salt, and variation of the molecular weight of the polymer ligands.