Abstract
Gold nanoparticles (AuNPs), synthesized by ns-pulsed laser ablation in liquid (ns-PLAL) in the absence of any capping agents, are potential model systems to study the interactions with biological structures unencumbered by interference from the presence of stabilizers and capping agents. However, several aspects of the physics behind these AuNPs solutions deserve a detailed investigation. The structure in solution of ns-PLAL-synthesized AuNPs was investigated in solution by means of small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Furthermore, the (dried) NPs have been examined using TEM. The analysis of the SAXS curve shows the presence of a large number of small aggregates with a fractal structure stabilized by strong long-range repulsive interactions. Fitting of the SAXS curve to a suitable “fractal model” allows the estimation of the features of the fractal including the fractal dimension d = 1.9. The latter allows to estimate the fraction of light scattered by fractals of different sizes and thus permits a fair comparison between the DLS and TEM data. Here, a stable abundant population of fractal clusters is reported reflecting a mechanism where primary AuNPs (size 7.6 nm) are forced to aggregate forming clusters during the collapse of the cavitation bubble. When these clusters are released in the aqueous phase, their large negative charge builds up repulsive interactions that prevent cluster-cluster aggregation imparting colloidal stability.
Highlights
Nanoparticles (NPs) made of noble metals are wellknown key materials in many basic and applied research fields, spanning from catalysis, optics, fuel cell and medicine, just to cite a few (Speder et al 2013, 2014; Silva et al 2014; Ramalingam et al 2014; Gellé and Moores 2019; Ferreira and Loh 2019; Ou et al 2019).Classical strategies to obtain metallic nanoparticles are based on the chemical reduction of corresponding oxidized cations by means of suitable reactants fulfilling the twofold roles of reductant and stabilizers
It should be stressed that despite a fractal dimension of 1.9 is often reported for fractals growing through diffusion-limited cluster aggregation (DLCA), the small clusters here observed are stable for weeks from the preparation
It is interesting to note that this mechanism fits the results reported in Ibrahimkutty et al (2012) and Reich et al (2017), where with in situ small-angle X-ray scattering (SAXS) experiment performed during the NS-pulsed laser ablation in liquid” (PLAL) processes, the creation of “primary” smaller NPs is subsequently followed by the formation of the aggregates after the maximum expansion of the cavitation bubble
Summary
Nanoparticles (NPs) made of noble metals are wellknown key materials in many basic and applied research fields, spanning from catalysis, optics, fuel cell and medicine, just to cite a few (Speder et al 2013, 2014; Silva et al 2014; Ramalingam et al 2014; Gellé and Moores 2019; Ferreira and Loh 2019; Ou et al 2019). Attributed to the presence of negative charges onto the surface of “naked” particles (Barcikowski and Compagnini 2013) (NPs have a strongly negative zeta potential), but the origin of those negative charges has only recently been addressed and is yet matter of debate (Jean-Philippe Sylvestre et al 2004; Muto et al 2007; Merk et al 2014; Palazzo et al 2017) In this contribution, we discuss the results of a small-angle X-ray scattering study performed on AuNPs solutions synthesized by ns-PLAL and the pieces of evidence of the arrangement of NPs in form of fractal clusters in the pristine solution. In Eq (5), P(q) is the form factor accounting for the intra-particle interference, while the structure factor S(q)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
