Supercrystal Formation of Gold Nanorods by High Pressure Stimulation

We demonstrate the pressure-induced formation of supercrystals made from PEGylated gold nanorods in aqueous suspension. Utilizing the combined effect of hydrostatic pressure and salt on the solubility of the organic PEG shell that passivates the nanorods, the reversible formation of two-dimensional hexagonal supercrystals has been observed by means of small angle X-ray scattering. The pressure dependence of the crystal lattice's structural parameters is determined. By time-resolved measurements performed after a pressure-jump, the growth process of the crystals is found to be finished already after a few seconds. The presented results demonstrate that by PEGylating nanoparticles pressure-induced homogeneous supercrystals can be formed for different particle shapes, in particular anisotropic nanorods, which determine the resulting lattice type.