title: Effect of nanomaterial and media physicochemical properties on Ag NM aggregation kinetics.
abstract: Nanomaterial (NM) aggregation is a key process determining their environmental, fate behavior and effects. Nanomaterials are typically engineered to remain kinetically stable; however, in environmental and toxicological media, NMs are prone to aggregation. The aggregation kinetics of NM is typically quantified by measuring their attachment efficiency (α) and critical coagulation concentration (CCC). Several studies measured α and CCC for Ag NMs with a major focus on investigating the effects of ionic strength, ion valency and natural organic matter, with few studies investigating other environmental factors such as light and dissolved oxygen and none investigating the effect of particle size, buffer type and concentration, or surface coverage by capping agent. A survey of recent research articles reporting CCC values for Ag NMs reveals substantial variation in experimental conditions and particle stability with CCC values of monovalent and divalent counterions covering a wide range (ca. 25 to infinity for monovalent counterions and 1.6 to infinity for divalent counterions). Here, we rationalize the differences in the CCC values for Ag NMs based on the variability in the experimental conditions, which includes NM and medium physicochemical properties. Capping agents determines NM stability mechanism with citrate, sodium dodecyl sulfate (SDS), and alginate stabilizing NM by electrostatic mechanism; whereas polyvinylpyrrolidone (PVP), casein, dextrin, tween, branched polyethyleneimine (BPEI), and Gum Arabic stabilizing NMs by steric mechanisms. The CCC values for Ag NMs with different capping agents follow the order citrate∼alginate∼SDS<casein<dextrin<PVP<tween<branched polyethyleneimine (BPEI)∼gum Arabic. For charge stabilized Ag NMs, the CCC increases with the decrease in NM size and buffer concentration and decreases with light irradiation. For sterically stabilized PVP-Ag NMs, the CCC increases with the coating concentration/surface coverage and completely coated Ag NMs do not undergo aggregation even at high salt concentrations.
authors: Center for Environmental Nanoscience and Risk, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States; Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
authors: Kamelia
authors: K
authors: Afshinnia
authors: Center for Environmental Nanoscience and Risk, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States; Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
authors: Mithun
authors: M
authors: Sikder
authors: Department of Epidemiology and Biostatistics, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
authors: Bo
authors: B
authors: Cai
authors: Center for Environmental Nanoscience and Risk, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States; Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States. Electronic address: mbaalous@mailbox.sc.edu.
authors: Mohammed
authors: M
authors: Baalousha
keywords: Aggregation kinetics; Attachment efficiency; Buffer concentration; Critical coagulation concentration; Silver nanomaterials; Size; Surface coating coverage