The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly use
agents—citrate and polyvinylpyrrolidone (PVP)—were investigated. Time-resolved dynamic light
(DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalen
electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excel
with the predictions based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and the Ham
of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10 J. Divalent electrolytes
efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical c
concentrations (2.1 mM CaCl and 2.7 mM MgCl vs. 47.6 mM NaCl). The PVP-coated AgNPs w
significantly more stable than citrate-coated AgNPs in both NaCl and CaCl , which is likely due to
repulsion imparted by the large, non-charged polymers. The addition of humic acid resulted in the
the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induce
electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing Na
concentrations of CaCl . Conversely, enhanced aggregation occurred for both nanoparticles at high
concentrations due to interparticle bridging by humic acid clusters.