Biomedical Engineering Reference
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tal applications such as various electronics, energy storages, and sensors. It has a
significant difference between tubular nanostructures and other forms (e.g., rods
and fibers) due to the enhanced surface-to-volume ratio of the tubular structure.
Most approaches for fabricating nanotubular structures, including CNTs, oxide
NRs, metal NRs, and CP NFs, focused on the use of hard-templates. Although these
methods permit controlled fabrication of the diameter and length, they are limited
by high-cost and complicated synthetic steps. Recently, alternative strategies, such
as soft-templates, have emerged, which simplify the fabrication process and facili-
tate large-scale production. Surfactant templates, a type of soft-template, can cre-
ate various micelles, such as nanoreactors, for synthesizing 1D CP NTs. A reverse
micelle, consisting of an aggregate of surfactant molecules containing a nanometer-
sized water pool in the oil phase, was introduced using sodium bis(2-ethylhexyl)
sulfoccinate (AOT) [
40
,
67
-
73
]. We demonstrated, for the first time, fabrication of
PPy NTs using a reverse micelle system, based on AOT; the PPy NT system was
characterized using polarizing optical microscopy (POM) [
34
]. Moreover, function-
alized PPy NTs were developed using a co-polymerization process; the stabilized
the electrical properties in the liquid state, providing efficient covalent bonding
between the biomolecules and sensing platforms.
Carboxylated polypyrrole nanotubes (CPNTs) were prepared by copolymeriz-
ing the pyrrole monomer and pyrrole-3-carboxylic acid (P3CA) in an AOT reverse
microemulsion system [
32
]. An AOT reverse cylindrical micelle phase is formed
by combining an apolar solvent (hexane) and FeCl
3
solution. Also, appropriate tem-
perature condition was calculated by a ternary phase diagram (Fig.
13.2a
; [
67
]). In
the first stage, a reverse cylindrical micelle phase was constructed by cooperative
interaction (charge-charge interaction) between Fe cations and AOT molecules to
produce a micelle having a diameter on the order of one nanometer. Metal salts in
the solution enable the growth of reverse micelles through critical micelle concen-
tration I and II. Second, a PPy and P3CA mixture was added a dropwise to the AOT/
hexane mixed solution containing a reverse cylindrical micelle phase. The polymer-
ization progressed rapidly using an oxidizing agent (iron cations) along the surface
of the reverse cylindrical micelles. This reaction can be observed with the change
of the colors from yellow to black during polymerization. Finally, CPNTs can be
obtained by washing process with an ethanol to remove residual reagents and AOT.
13.3.2
Characterization of CPNTs
To confirm the CPTNs, X-ray photoemission spectroscopy (XPS) was observed.
Figure
13.2b
displays the identification of CPNTs and pristine PPy NTs. The sur-
vey scan spectrum showed the presence of the principal C 1s, O 1s, and N 1s core
levels. The representative O 1s peak of the CPNTs was characterized by a chemi-
cal map of the XPS (Fig.
13. 2c
). The amount of O 1s peak was ca. 32 % and it is
consisted of three components centered at 531, 532.2 and 533.3 eV, corresponding
to alcohol, carboxyl, and ether-type oxygens respectively. Field-emission scanning
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