Biomedical Engineering Reference
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conducted by Wagner et al. [70]. Two common ionic liquids: [BMIM]
[PF
] and [BMP][Tf
N] have been used as the solvent as well as ACN
6
2
+ TBAPF
for comparison. Polymerization was greatly improved in
[BMIM][PF
6
]. Results from doping studies showed that n-doping
in [BMP][Tf
6
N] exhibited the best electrochemical response. In
addition, the use of ionic liquids enabled spectroscopic studies of
PPP films at higher doping levels in contrast to the conventional
organic electrolyte.
2
3.4 SYNTHESIS OF POLYMER COMPOSITES AND
CARBON-BASED NANOMATERIALS IN IONIC
LIQUIDS
Functionalized single-walled carbon nanotubes (SWNTs) have
attracted attention because of their promising applications in
photovoltaic devices [71-73]. Since SWNTs are n-type materials and
PANI is both stable and has sufficient electron-donating properties,
electrochemical functionalization of carbon nanotubes with PANI
has been studied [74-76]. In order to achieve functionalized SWNTs
in larger quantities, Wei et al. used [BMIM][PF
] mixed with 1 M
trifluoroacetic acid [77]. SWNTs were mixed and grind with [BMIM]
[PF
6
] containing the monomer and the acid. The electrochemical
polymerization was done by potential scanning with 300 cycles on
modified ITO substrate. After 50 cycles, a growth of PANI around
the nanotubes was observed. Figure 3.5 presents SEM images of
SWNTs and PANI wrapped around them. The possible mechanism
of functionalization is also shown in Fig. 3.5. Charged radicals
produced during polymerization can make covalent bonding with
the surface of the nanotube [78]. This suggestion was confirmed by
changes in the carbon D and G band intensities in the Raman spectra.
IL provided a good environment for obtaining sufficient quantities
of PANI/SWNTs composites, since SWNTs dissolve more easily in ILs
than in aqueous or conventional organic solvent. This can probably
be attributed to cation/π-electron interactions [79]. Also, the high
dielectric constant of ionic liquids may be an important factor in
dispersibility of nanomaterials since it leads to shielding of the
van der Waals interactions.
6
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