Behavior of au nanoparticles under pressure observed by in situ small-angle X-ray scattering

The mechanical properties and stability of metal nanoparticle colloids under high-pressure conditions are investigated by means of optical extinction spectroscopy and small-angle X-ray scattering (SAXS), for colloidal dispersions of gold nanorods and gold nanospheres. SAXS allows us to follow in situ the structural evolution of the nanoparticles induced by pressure, regarding both nanoparticle size and shape (form factor) and their aggregation through the interparticle correlation function S(q) (structure factor). The observed behavior changes under hydrostatic and nonhydrostatic conditions are discussed in terms of liquid solidification processes yielding nanoparticle aggregation. We show that pressure-induced diffusion and aggregation of gold nanorods take place after solidification of the solvent. The effect of nanoparticle shape on the aggregation process is additionally discussed. We thank Professor Jan Dhont for helpful comments about nanoparticle diffusion in solid ethanol. F.R. acknowledges financial support from Projects PID2021-127656NB-I00 and MALTA-Consolider Team (RED2018-102612-T), and L.M.L.-M. from PID2020-117779RB-I00 and MDM-2017-0720, from the State Research Agency of Spain, Ministry of Science and Innovation. C.M.-S. acknowledges funding from the Spanish Ministry of Universities and the European Union-NextGeneration EU through the Margarita Salas research grant (C21.I4.P1). We acknowledge SOLEIL for the provision of synchrotron radiation facilities, and we would like to thank Dr. Javier Pérez, beamline supervisor, for assistance in using beamline SWING (proposals 20191731 and 20210678). This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation program under the SINE2020 project, grant agreement no. 654000.