Biology Reference
In-Depth Information
Solvophobic
interactions
are
an
attractive
force
between
32
nanocrystals, which arise from poor solvent effects.32
Addition of a
poor solvent into a stable colloidal solution decreases the solvent
shell thickness and increases the surface tension at the interface
between the colloidal nanocrystals and solvents. When two particles
touch each other, surface overlapping leads to a decrease in the total
surface area of these two particles as well as their surface energy,
which results in an attractive interaction. The energy of solvophobic
interactions can be given as follows:
E
= 2A
γ 4πrh
γ
(13.6)
SP
i
o
where
solvent interface.
According to the extended DLVO theory (named after Derjaguin,
Landau, Verwey, and Overbeek), the total interaction between two
colloidal particles is the superposition of all these attractive and
repulsive interactions.
g
is the surface tension at the nanocrystal
−
24,28
Therefore, the total interaction energy is
the summation of the energies of all these interparticle interactions
and can be expressed as follows:
(13.7)
When repulsive forces are dominant, no effective binding
takes place between the two interacting colloidal particles. When
attractive interactions prevail and the total interaction energy (E
E
= E
+ E
+ E
+ E
TOT
L
E
S
SP
)
TOT
is greater than the thermal energy (3/2 k
T), the two particles
bind together after collision, leading to the nucleation and growth
of superparticles.
B
31
In practice, it is very easy to create binding
between nanocrystals and trigger the nucleation of superparticles.
For example, increasing the ionic strength of a solution can trigger
the aggregation of charged colloidal particles, while the aggregation
of noncharged particles takes place at a high surface tension
induced by the addition of a poor solvent.
11,14,31
However, it is a
very difficult task to prevent the unlimited growth and/or fusion of
particle aggregates. These effects often lead to a rapid precipitation
of particle aggregations, resulting in particle aggregates that exhibit
poorly defined structures with random sizes and shapes.
−
To limit these effects, one has to slow down the rate of nanocrystal
aggregation, and/or create a particle surface functionality to
prevent
33
35
1,19,23
−
25
In general, the
nanocrystal aggregation rate is under kinetic control, and it is
determined by the product of the particle collision frequency and
the successful binding rate of each collision.
the
fusion
of
superparticles.
31
It is difficult to
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