Interactions of sub-five-nanometer diameter colloidal palladium nanoparticles in solution investigated via liquid cell transmission electron microscopy

Inter-particle interactions play important roles in controlling the structures, dispersion state and chemo-physical properties of colloidal nanoparticles (NPs) in liquid media. In this work, we prepared palladium (Pd) NPs with an average diameter of ∼4.6 nm in situ inside the liquid cell, and investigated their coupled diffusion and aggregation behaviors through liquid cell transmission electron microscopy (LCTEM). Via analyzing the interaction energies and forces, we derived the effective working range for repulsive double layer interaction experimentally, a value larger than two times the Debye length, suggesting a different interaction behavior of sub-5 nm NPs from that of colloidal NPs in larger sizes. Our results provide insights for the interactions between colloidal ultrafine nanoparticles in solution and will also shed light on the precisely controlled assembly of colloidal nanocrystals for practical applications.