posted on 2020-04-23, 17:09authored byDebora Monego, Thomas Kister, Nicholas Kirkwood, David Doblas, Paul Mulvaney, Tobias Kraus, Asaph Widmer-Cooper
We
report on the colloidal stability of nanoparticles with alkanethiol
shells in apolar solvents. Small-angle X-ray scattering and molecular
dynamics simulations were used to characterize the interaction between
nanoparticles in linear alkane solvents ranging from hexane to hexadecane,
including 4 nm gold cores with hexadecanethiol shells and 6 nm cadmium
selenide cores with octadecanethiol shells. We find that the agglomeration
is enthalpically driven and that, contrary to what one would expect
from classical colloid theory, the temperature at which the particles
agglomerate increases with increasing solvent chain length. We demonstrate
that the inverted trend correlates with the temperatures at which
the ligands order in the different solvents and show that the inversion
is due to a combination of enthalpic and entropic effects that enhance
the stability of the ordered ligand state as the solvent length increases.
We also explain why cyclohexane is a better solvent than hexadecane
despite the two having very similar solvation parameters.