Biomedical Engineering Reference
In-Depth Information
13.2.1
Hard-Template Methods
The hard-template method, one of the most facile synthesis methods, is advanta-
geous for designing nanomaterials, such as core/shell materials, nanoparticle (NPs),
and nano-capsules [
53
-
56
]. One-dimensional CP nanomaterials, including nanorods
(NRs), nanotubes (NTs), and nanofibers (NFs), can be easily tailored by hard-tem-
plates, such as anodic aluminum oxide (AAO) and polycarbonate (PC) membranes.
Compared with conventional structured or patterned templates, AAO membranes
are widely used in various fields, due to their controllable pore and diameter sizes.
For example, polypyrrole (PPy), polyaniline (PANi), polythiophene (PT), and poly
(3,4-ethylenedioxythiophene) (PEDOT) NTs have been fabricated using hard tem-
plates for electronic devices. Moreover, these 1D CP nanomaterials can be designed
not only with fixed diameters and lengths, but also with controlled wall-thicknesses.
Park et al. fabricated 1D CP nanomaterials as a transducer in chemical sensor ap-
plications (Fig.
13.1a
; [
57
]).
13.2.2
Soft-Template Methods
Recently, various 1D CP nanostructures have been constructed using soft-template
methods, such as surfactant, liquid crystalline polymer, cyclodextrin, and function-
alized polymer techniques [
58
-
61
]. Importantly, surfactants, which imply cationic,
anionic, and non-ionic amphiphiles, are mostly used for the formation of micelles as
a nanoreactor [
40
,
62
]. The nanoreactors can be formed in micro-emulsions, which
are macroscopically homogeneous mixtures of oil, water, and surfactant, leading to
a useful medium for polymerization reactions. Thus, this technique allows the prep-
aration of controllable 1D CP nanomaterials with a narrow size distribution, using
cylindrical micelle and lamellar phases. We have synthesized various 1D CP nano-
materials, such as PEDOT NTs, PEDOT NRs, and PPy NTs, using soft-template
methods. For example, Jang et al. demonstrated 1D PPy NTs using reverse micelle
systems and provided their fabrication mechanism (Fig.
13.1b
; [
34
,
63
]). It is im-
portant to note that the polymerization process in soft-template methods is kineti-
cally and thermodynamically unstable, due to Ostwald ripening, growth by collision
between monomer droplets, and monomer consumption during polymerization.
13.2.3
Template-Free Methods
Template-free approaches have been studied extensively for the fabrication of 1D
CP nanomaterials, because they are very straightforward, with no specific sacri-
ficial template [
64
-
66
]. However, these approaches are limited to particular pre-
cursor materials. Compared with the other methods (i.e., soft and hard-templates),
these methods can be used to fabricate simple, uniform, and high-quality nano-
materials. We have also demonstrated the fabrication of various shape-controlled
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