Tuning the Interaction of Nanoparticles from Repulsive to Attractive by Pressure

We report a high pressure small-angle X-ray scattering (SAXS) study on concentrated aqueous suspensions of gold nanoparticles coated with a poly(ethylene glycol) (PEG)-based ligand shell. Analyzing the experimental SAXS data with a liquid-state theory approach, we find a pressure-induced transition of the interparticle interactions from repulsive to attractive in the pressure range from 1 to 4000 bar that also depends on the particle concentration. This transition is related to structural changes of the ligand shell which is compressed with increasing pressure. Our study highlights the important, yet unexplored role of pressure for the interaction of nanoparticle systems