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28
of the thioether mediator.
further identified
that the activation energy for superparticle formation is only
In addition, Zhong
et al.
−
1.3
40
kcal/mol,
which is much smaller than the bonding energy of
thioether
gold coordination bonds. Therefore, it is unlikely that the
gold superparticle formation is through particle cross-linking by the
mediators.
−
28
Figure 13.3
Schematic illustrations of the mediation-template strategy
for
2
-mediated assembly of
1
-capped gold nanocrystals (
1
/
Au). From Ref. [28] with permission.
, we herein
identified that the driving force for gold-superparticle formation is
solvophobic interactions, which are induced by thioether mediators.
In this synthesis, the bulky hydrocarbon chains of TOA ligands make
gold nanocrystals dispersible in toluene.
On the basis of the results from Zhong
et al.
The replacement of
TOA with the bulky and short thioether mediators decreases the
number of hydrocarbon chains on these gold nanocrystals, and
induces repulsive surface tension between the nanocrystal ligand
shell and solvent media, thus resulting in solvophobic interactions
in the colloidal dispersion. Therefore, partial ligand exchange with
thioether mediators leads to the formation of active species for the
nucleation and growth of gold superparticles. According to this
mechanism, the interparticle distance in the superparticles should
be determined by the length of TOA (
24,28
∼
2.0 nm), which is identical
The identification of
solvophobic interactions as a driving force is also consistent with
the small superparticle formation enthalpy measured by Zhong
to that from Zhong's experimental data.
24,28,40
et
al.
More importantly, solvophobic interactions should play a major
role in the formation of spherical superparticles, which exhibit a
minimized surface energy.
40
27
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