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0Irreversible aggregation of Au nanoparticles in aqueous colloids resulting in formation of chain-like structures during solvent
evaporation
A.V. Simakin1*, A.O. Dikovskaya1, I.V. Baimler1, S.V. Gudkov1
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilova Street,
119991 Moscow, Russia
According to DLVO model, nanoparticles in a colloidal solution have a layer of adsorbed environmental components on their surface, which affects their properties and characteristics [1]. If particles are not fully coated during the synthesis process, aggregation may occur. Gold nanoparticles, known for their stability, have a significant electrical charge and a layer of gold hydroxide on their surface [2]. As the nanoparticles approach each other, the dipole-dipole potential becomes more significant, leading to an increasing force of attraction and aggregation [3]. However, this approach does not provide a general explanation for the irreversible formation of aggregates. Although many aspects of aggregation have been studied, the fundamental physico-chemical mechanisms underlying reversible and irreversible aggregation of metal nanoparticles in liquids remain poorly understood.
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Fig. 1. (A) Dependence of the concentration of Au NPs on evaporation time, (B) TEM images of the formation of chain-like aggregates of Au NPs.
This work demonstrates the existence of a critical concentration limit for the stability of aqueous colloidal solutions of gold nanoparticles without use of surfactants (Fig.lA). It was shown that as the volume of the solvent in the solution decreases, the size and concentration of the nanoparticles change in a non-monotonic manner. When the concentration of nanoparticles in a solution containing gold nanoparticles with a diameter of approximately 15 nanometers reaches approximately 1013 NPs/mL, intense aggregation occurs, forming elongated aggregates of nanoparticles (Fig.1B). This was confirmed using transmission electron microscopy and optical absorption spectroscopy. The nanoparticle aggregation process has been shown to be irreversible, and the zeta potential of the colloid does not change during this process.
The research was supported by Russian Science Foundation (Project № 24-22-00363, https://rscf.ru/project/24-22-00363).
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[2] G. Palazzo, G. Valenza, M. Dell'Aglio, A. De Giacomo, On the stability of gold nanoparticles synthesized by laser ablation in liquids, Journal of colloid and interface science, 489, 47-56, (2017).
[3] H. Zhang and D. Wang, Controlling the growth of charged-nanoparticle chains through interparticle electrostatic repulsion, Angewandte Chemie, 120(21), 4048-4051, (2008).
