Time and Temperature Effects on the Digestive Ripening
of Gold Nanoparticles: Is There a Crossover from Digestive Ripening
to Ostwald Ripening?
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Abstract
The effects of time and temperature
on the gold nanoparticle sizes
obtained by digestive ripening have been investigated. In digestive
ripening, a polydisperse colloid, upon refluxing with a surface-active
ligand in a solvent, gets converted to a nearly monodisperse one.
In this study, a polydisperse gold nanoparticle system was heated
in 4-tert-butyltoluene with
hexadecanethiol at different temperatures, viz., 60, 90, 120, 150,
and 180 °C for different time periods, and the trends in particle
size variations were recorded. At lower temperatures such as 60 and
90 °C, after the initial narrowing of the size distribution,
the particle sizes remain constant even though the refluxing step
is continued for 24 h, substantiating the prevalence of the digestive
ripening process. However, at elevated temperatures (120, 150, and
180 °C) particle sizes grow continuously, indicating a deviation
from the digestive ripening behavior to an Ostwald ripening-type phenomenon