Temporal Changes in Interparticle Interactions Drive the Formation of Transiently Stable Nanoparticle Precipitates

We demonstrate the power of fine-tuned interparticle interactions, emanating from appropriately functionalized surfaces, in creating self-assembled structures that show a transient switching between completely precipitated and redispersed stages of nanoparticles (NPs). The pH-dependent temporal changes in the strength of electrostatic interactions are explored to unveil a transient self-assembly response in plasmonic NPs. The assembly process was triggered by the electrostatic attraction between positively charged gold NPs (AuNPs) and an aggregating agent, ethylenediaminetetraacetic acid (EDTA). The autonomous changes in the pH and ionic strength of the solution, under the influence of atmospheric CO₂, weaken the aggregating ability of EDTA and initiate the complete disassembly of [+] AuNP-EDTA precipitates. The use of a nondestructive mode of autonomous disassembly helped in achieving some of the desirable feats in the field of transient self-assembly such as easy removal of waste, formation of a transiently stable precipitate state, and negligible dampness in redispersion. The chemical strategy adopted in the present work, to introduce transientness, can act as a generic tool in creating the next generation of complex matter.