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and 20 min, respectively; Yoshida et al., 2010). The vapor pressure of 5CB is
reported to be less than 0.23 Pa at room temperature (Deschamps et al., 2008),
which enables gold deposition without any noticeable evaporation of the host.
The pure 5CB appears white at room temperature because of light scattering,
while the gold-deposited samples exhibit a brown-reddish color (deposition
time dependent). The extinction spectra of the material shown in Figure 7.15b
demonstrates that the color of the LC is attributed to the local surface plasmon
resonance of gold, which is observed as a slight shoulder at around 520 nm. A
linear relationship between the deposition time and the concentration of the
gold nanoparticles was revealed (inset in Fig. 7.15b). It should be noted that
the nanoparticles were reported as very stable in the LC phase and did not
show any observable changes for at least 3 months (Yoshida et al., 2010).
Microscopy images (data not shown) were evidence for obtaining spherical
nanosized particles with a mean diameter of 2.9 nm and a standard deviation
of 0.6 nm. It has been emphasized that the maximum diameter to which the
nanoparticles grow is limited to a certain value determined by the physical
properties of the host LC, such as its wettability and elastic constants. Finally,
the electrooptic properties of a twisted nematic cell with the specifi c gold
nanoparticles show remarkable improvement.
7.3
CONCLUSIONS
In the past several decades, many methods have been developed to synthesize
nanostructured materials with controlled size, shape, dimensionality, and struc-
ture, including lithographic techniques and hard-template methods. However,
the use of soft (liquid crystalline) templates for nanomaterial syntheses exhib-
its many incomparable advantages over other methods. The diversity of LC
mesophases, particularly those of lyotropic type, has been utilized as directing
agent, direct or reverse templates, and proven to be useful routes to prepare
porous organic materials, oxides, metal/alloy, and others. So far, the TLCs have
not yet been used to as great (an extent for the synthesis of metallic, magnetic,
or semiconducting nanoparticles as the lyotropic LCs have.
One of the most attractive features of these methods is the versatility of
the resultant structure of the nanomaterials, transferred from the LC tem-
plates to the desired materials. The reactants are confi ned in the limited dimen-
sion of the LC and the structures of long-chain order affect the nucleation and
growth processes of the products, which could be applied to control the syn-
thesis of the nanomaterials with desired morphologies.
As a result, rich morphologies of the synthesized nanomaterials are obtained,
including spherical particles, hollow nanostructures, 1D nanowires, nanorods
and nanotubes, and 2D ordered arrays.
We demonstrated that among those three main methods based on liquid
crystalline systems, the direct and reverse templating methods were the supe-
rior ones. These preparation techniques were shown to be easily reproducible
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