Biology Reference
In-Depth Information
1,20,21
building blocks and solvent media.
This synthetic approach
utilizes water-soluble nanocrystal micelles as precursors for the
synthesis of supercrystalline colloidal superparticles. The formation
of nanocrystal micelles was driven by the hydrophobic van der Waals
interactions between the hydrocarbon chains of nanocrystal ligands
(e.g., oleic acid on Fe
nanocrystals) and the hydrocarbon chains
of the surfactant (e.g., dodecyl trimethyl-ammonium bromide, DTAB,
see Fig. 13.9). Colloidal superparticles form upon the introduction
of the nanocrystal micelles into an ethylene glycol solution.
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On the basis of this approach, we have synthesized colloidal
supercrystalline superparticles from nonpolar-organic-solvent
dispersible nanocrystals of a variety of chemical composition. The
resulting colloidal Fe
superparticles are highly dispersible in
polar solvents such as ethanol and water. These superparticles—
like those made using the microemulsion templates—possess a
dramatically different surface functionality from their building
blocks, which plays a key role in the formation of a supercrystalline
structure. In addition, superparticle formation in a CIS synthesis is
a kinetically controlled process, thus it allows particle size control
according to Eq.13.10.
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nanocrystals as a
model, we have identified that there are two major stages in the
superparticle formation in a typical CIS synthesis: (1) aggregation
and (2) crystallization (Fig. 13.9a). Transmission electron microscope
(TEM) shows that the Fe
Using oleic acid functionalized 5.8 nm Fe
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particle micelles were monodispersed
with a nearly identical size to their nonpolar-solvent-dispersible
counterparts (Fig. 9b,c). After the nanocrystal micelle solution
was injected into a poly(vinyl pyrrolidone) (PVP) ethylene glycol
solution, the van der Waals interactions between nanocrystal ligands
and surfactants were weakened, and then these nanocrystal micelles
decomposed owing to the loss of DTAB molecules into the ethylene
glycol solution (Fig. 13.9d,e). As a result, a solvophobic interaction
between nanocrystal surface ligands and ethylene glycol/water
solvent molecules was induced, leading to nanocrystal aggregation
and the formation of superparticles. Surprisingly, the superparticle
formation is a very rapid process. TEM studies show that nearly all
the 5.8 nm Fe
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nanocrystals grew into superparticles within 1 min
after the injection of nanocrystal micelles, and then afterwards the
size of the superparticles did not change substantially. In addition,
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