title: Kinetics of aggregation and growth processes of PEG-stabilised mono- and multivalent gold nanoparticles in highly concentrated halide solutions.
abstract: 5-6 nm gold nanoparticles were prepared by hydrolytic decomposition of [NMe4][Au(CF3)2] and functionalized in situ with mono- and multivalent thiolated PEG ligands. Time-dependent changes of the nanoparticles were monitored in aqueous NaCl, NaBr, and NaI solutions by UV-Vis spectroscopy, TEM, and HRTEM. The purely sterically protected particles are stable in ≤1 M NaCl and NaBr solutions, regardless of the valence of the ligands. At higher concentrations (≥2 M), the monovalent stabilized particles show minor reaction limited colloidal aggregation. In NaBr but not in NaCl solutions a minor Ostwald ripening also occurs. The divalent stabilized particles remain colloidally stable in both halide solutions, even if the temperature is raised or the concentration is increased above 2 M. In ≤1 M aqueous NaI solutions the particles remain stable. Above, the monovalent stabilized particles undergo an oxidative reaction, resulting in a time-dependent shift and broadening of the absorbance spectrum. Finally, this process slows down while the width of the spectra slightly narrows. The kinetics of this process can be described by a two-step sigmoidal process, comprising a slow induction period where active species are formed, followed by a fast growth and aggregation process. The increasing concentration of fused structures from the aggregates during this process results in a narrowing of the size distributions. The divalent stabilized particles show only some minor broadening and a slight shift of the absorbance spectra in ≤3 M NaI solutions. These observations confirm the excellent stability of the multivalent stabilized particles from this chloride-free particle synthesis.
authors.affiliation: Institut für Chemie u. Biochemie, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany. cmgraf@zedat.fu-berlin.de.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Stein
authors.forename: David
authors.initials: D
authors.lastname: Zopes
authors.forename: Madlen
authors.initials: M
authors.lastname: Schmudde
authors.forename: Ralf
authors.initials: R
authors.lastname: Schneider
authors.forename: Ahmed
authors.initials: A
authors.lastname: Mohsen
authors.forename: Christian
authors.initials: C
authors.lastname: Goroncy
authors.forename: Sanjay
authors.initials: S
authors.lastname: Mathur
authors.forename: Christina
authors.initials: C
authors.lastname: Graf