Chemistry Reference
In-Depth Information
Figure 7.10
Schematic representation of nanoparticle synthesis utilizing LLCs as
nanoreactors. [Adapted from Karanikolos et al., (2006).]
solution is mixed with an appropriate amount of liquid crystalline host to
form the desired LLC phase. Then, the nanoparticles aggregate into clusters
to form a single nanostructure, which ideally will take on the shape of the
original LLC nanodomain (as illustrated in Fig. 7.10). When successful tem-
plating effect occurs, the columnar phases will form tube, wire, or rodlike
nanostructures, whereas cubic and lamellar phases usually will result in spher-
ical or disklike nanostructures (Ding and Gin, 2000; Karanikolos et al., 2006).
Finally, the produced nanoparticles can be collected through centrifugation
or fi ltering.
Dellinger and Braun (2004) have used LLCs to synthesize nanoparticles.
They exploited the restricted dimensions of the hydrophilic and hydrophobic
domains (2-10 nm) in order to selectively soluble the reagents in only one of
the nanoscopic dimentions. The authors new approach included synthesis of
Bi and PbS (lead sulfi de, a semiconductor compound) nanoparticles by bring-
ing together reactants via the shear mixing of two liquid crystals, while the
mixture containing dissolved reactants that are selectively soluble in one of
the two phases (Dellinger and Braun, 2004).
In the case of BiOCl synthesis both lamellar and hexagonal LLC hosts were
used (Dellinger and Braun, 2004). The LLC was added to aqueous BiCl
3
while
simultaneously heating and stirring, and upon cooling to room temperature
BiOCl was precipitated through the diffusion of ammonia into the LLC lattice.
It was found that the lamellar phase produced spherical 5-nm particles, whereas
the hexagonal LLC phase formed monodisperse 100 - nm - wide and 250 - nm -
long rods. Furthermore, an isotropic fl uid host yielded disk-shaped particles
with 50- to 250-nm diameters (Dellinger and Braun, 2004).
PbS nanoparticles were prepared by shear mixing of a liquid crystal con-
taining solutions of Pb(NO
3
)
2
or Pb(CH
3
COO)
2
(
0.005 - 0.1 M) with addi-
tional LCs containing saturated solutions of the extrinsic reducing agent H
2
S
(
∼
0.1 M) produced by bubbling H
2
S through water. As a result an LC that
contained PbS nanoparticles was formed.
∼
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