Chemistry Reference
In-Depth Information
Figure 7.11 depicts micrographs of PbS nanoparticles produced from lead
nitrate via shear mixing in the hexagonal, lamellar, and inverse hexagonal
phases based on the nonionic amphiphile oligo(ethylene oxide)10 oleyl ether
(Dellinger and Braun, 2004). By altering the liquid crystalline phase from
hexagonal to lamellar to inverse hexagonal, the geometry of the aqueous
domains has been modifi ed from
3D continuous nanoreactors
to sheetlike
2D
nanoreactors
to rodlike
1D nanoreactors
. The size of the nanoparticles was
clearly dependent on the morphology of the phases. When the hexagonal
phase was used, with a 3D continuous medium, the particles produced were
somewhat polydispersed and exhibited the cubic morphology common for
PbS. Changing to lamellar and then to inverse hexagonal phases resulted in
the production of spherical morphology particles of reduced size.
Qi et al. (1999) have been demonstrated that ribbons of silver nanoparticles
can be synthesized in lamellar LCs based on tetraethylene glycol monododecyl
ether (C
12
E
4
) and aqueous silver ion solution by the reduction of the silver
ions using the surfactant itself as reductant.
The ribbons were found to consist of close-packed silver nanoparticles
about 2-3 nm and a few larger silver nanoparticles distributed or attached on
the ribbons. The authors revealed that altering the surfactant concentration
(e.g., decreasing C
12
E
4
content, which increases the water layer thickness) did
not affect the size of the smaller particles forming the ribbons; however, it had
a direct impact on the proportion and/or size of the larger particles (Qi et al.,
1999). After 20 days, the ribbons of silver nanoparticles were formed (
∼
300 nm
wide and 7
μ
m long) twisted and folded, thereby forming complex 3D
confi guration.
In other research, reverse hexagonal LCs were used as template to synthe-
size nanowires (e.g., ZnS) by
-ray irradiation (Jiang et al., 1993). However,
due to the random orientation of the hexagonal cylinders, the resultant nanow-
ires were relatively short (
γ
m). An additional method for the formation of
nanowires was demonstrated by Huang et al. (2002). The authors showed that
cuprite (Cu
2
O) semiconductor nanowires can be fabricated by electrodeposi-
tion within H
II
LLC based on sodium bis(2-ethylhexyl) sulfosuccinate (AOT)
(Huang et al., 2002). By changing the time of electrodeposition, they exhibited
the ability to control the growth of the nanowires up to tens of micrometers.
Upon relatively short electrodeposition time (1 h) a large number of nanow-
ires of 3 - 5
<
2
μ
m length were obtained (Fig. 7.12a) while longer deposition time
(2 h) resulted in longer and higher diameter nanowires (10
μ
m length and
100 nm diameter; Figs. 7.12b and 7.12c; Huang et al., 2002). The diameter
values of the nanowires were also revealed to be controlled by adjusting the
water-to-surfactant ratio. It should be noted that in the absence of LLC per-
forming as a template for this synthesis only micrometer-sized copper crystals
were produced from bulk CuCl
2
aqueous solution at the same conditions.
Additionally, a short electrode distance during electrodeposition was shown
to improve the alignment of the liquid crystalline phase for producing nanow-
ires with a high aspect ratio (Huang et al., 2002).
μ
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