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Abstract
from the obtained results in the present work, the following
conclusions can be considered:-
from the TEM results:
1. The particle size of PANI nanoparticles was increased from
3.2 to 10 nm as the oxidation time increased from 30 to 120
from the obtained results in the present work, the following
conclusions can be considered:-
from the TEM results:
1. The particle size of PANI nanoparticles was increased from
3.2 to 10 nm as the oxidation time increased from 30 to 120
min.
2. The PANI nanofibers were grow extensively with the length
of several hundred nanometers and diameter around 30-60
nm.
3. The PANI nanotubes grow extensively with length ranges
from sub-micrometer to several micrometers. The inner
diameter of nanotubes is around 30-40 nm and outer diameter
around 50-70 nm.
X-Ray Diffraction Pattern Results:
1. The degree of crystallinity and particle size of PANI
nanoparticles are increased with increasing oxidation time.
While d-spacing, inter-chain separations are decreased.
2. The crystallinity of PANI nano-particles and fibers are the
same. This is due to the formation of PANI nano-particles
and fibers don’t require any template.
Conclusion
141
3. PANI nanotubes have high crystallinity than PANI nanoparticles
and fibers. This indicated that the crystallinity of
PANI nanotubes depend on the template used.
Infrared spectra
1. For the PANI nanoparticles, with increasing oxidation time,
some vibrational bands are shifted to lower wavenumbers.
Due to the H-bonding interaction between polyaniline chains
and hydrochloric acid, and hydrogen bonding between the
amine and imine nitrogen sites in the PANI chain. The
intensity ratio of (I1575/I1492) increases with increasing
oxidation time. The intensity ratio indicates that the PANI
nanoparticles in emeraldine salt form.
2. FTIR data revealed that, the spectra of PANI nano-particles
and fibers are the same, with slight shift in some bands. This
indicates that PANI nanofibers were formed in emeraldine
salt form.
3. For PANI nanotubes, the N-H stretching vibration band
shifted from 3233 cm-1 for nanoparticles to 3252 cm-1. The
two new bands appeared at 2922, 2851 cm-1 are due to the
stretching vibration of CH2 group. The band appeared at
1044 cm-1 assigned to COOH groups for carboxylic acid in
the PANI. This is proved that the hydrogen bond with N-H
is formed through the OH group of the carboxylic acid with
Conclusion
142
PANI chain. The interchain hydrogen bonding between
amine and imine nitrogen sites of separate PANI chains has
been proposed to be a driving force in the formation of the
PANI self-assembly nanotubes. And indicate that PANI
nanotubes is formed by template (carboxylic acid).The
disappearance of this bands in the infrared spectra of PANI
nano-particles and fibers, are due to the formation of PANI
nano-particles and fibers don’t need any template to form.
This results is in agreement with the TEM discussion.
4. The intensity ratio of (I1575/I1492) of PANI with different
shape indicates that the PANI nanotubes have high oxidation
state than PANI nano-particles and fibers.
Electronic Spectra:
1. For PANI nanoparticles, it was noticed that by increasing
oxidation time the absorption bands at 326 and 610 nm are
shifted to 340, and 635 nm. This indicated that with
increasing oxidation time the particle size and the
conjugation length of PANI chain increased.
2. The intensity ratio of (I610/I326), which referred to the degree
of oxidation state in PANI chain was calculated. It was
found that, the intensity ratio increased with increasing
oxidation time. This means that the benzeniod unit changed
Conclusion
143
into quinoid structure in PANI and the PANI was formed in
emeraldine salt (ES) form.
3. It was noticed that, the effect of solvents (DMF, mixture of
(DMF-methanol) and deionized water) on PANI
nanoparticles at different oxidation time and PANI nanofibers
and tubes leaded to slight shift in the position of all
absorption bands and new bands appeared in the
UV-Vis spectra. This change indicates that PANI chain
may have different conformations and different conjugation
lengths in different solvents.
4. A new band appeared in the UV-Vis spectra of PANI with
different particle size and shape at 425nm in mixture (DMFmethanol)
solvent and deionized water as a solvent. This
band is corresponded to the polaron-π* transition, which is
characteristic the protonated PANI.
5. The new absorption band appeared in deionized water as a
solvent at 750nm with extended tail is attributed to
π-polaron transitions of PANI backbone. This indicates that
the bipolarons and radical cation states are formed on the
polyaniline backbone chain. This means that PANI is in the
doped state.
Conclusion
144
6. Comparing the UV-Vis spectra of PANI nanotubes with that
of PANI nano-particles and fibers in deinoized water as a
solvent, it is clear that the absorption peaks for PANI
nanotubes were appeared at higher wavelength than PANI
nano-particles and fibers. The absorption band at 820nm in
the UV-Vis spectra of PANI naontubes is broader and
shifted to higher wavelength than the band tail around
750nm in PANI nano-particles and fibers. This is indicated
the higher doping level of PANI nanotubes.
7. The π-polaron band at 804 nm is broaded with the band at
680 nm in the UV-Vis spectra of PANI nanotubes in
mixture of (DMF-Methanol) solvent. This indicates
presence of the transition of the excitonic to bipolaronic.
And this leads to increase in the electronic mobility. The
results indicated that the doped level of PANI nanotubes is
higher than the doping level of PANI nanofibers, and PANI
nanotubes is more delocalized.
8. The discussion of UV-Vis absorption patterns indicated
that, the formation of PANI with different shapes in
emeraldine salt (ES) form.
9. from the optical band gap calculations, it was shown that
for all investigated samples, the transition was direct
transition.
Conclusion
145
10. For PANI nanoparticles, the band gap shifted to lower
values with increasing particle size.
11. For PANI nano-fibers and tubes, the values of band gapes
are 3.26 and 2.74 eV respectively.
12. It is noticed that, polyaniline (PANI) haven’t constant
values of optical bandgap, it depend on the doping and the
polymerization method.
Electrical Conductivity:
1. The DC conduction mechanism were studied by Current-
Voltage Characteristics and it was found that there is one
region, where Ohm’s law is obeyed. It is also found that, the
current (I) increased with increasing particle size for PANI
nanoparticles at the same value of the applied voltage.
2. The DC electrical conductivity at room temperature
increases with increasing oxidation time and particle size
for PANI nanoparticles. The conductivity of PANI nanotubes
and fibers is higher than that of PANI nanoparticles.
3. The conductivity of PANI can be represented as a sum of
the interchain and intrachain conductivity. It depends on the
level of doping, conjugation length of PANI chain and on
the degree of crystallinity. The conductivity can be
Conclusion
146
explained on the basis of the formation of polarons and
bipolarons.
4. The DC electrical conductivity has been measured in the
temperature range from 25-177oC. The obtained results
revealed that all the investigated samples posses
semiconducting behavior.
5. The observed DC conductivity data have been analyzed in
the light of existing theoretical models. The conduction
mechanism of the investigated samples shows Arrhenius
model. The conduction in these samples occurs through a
thermally activated process.
6. The conductivity of PANI nanoparticles increased
monotonically at higher temperature with increasing particle
sizes. The conductivity of PANI nano-fibers and tubes at
higher temperature are higher than that of PANI
nanoparticles.
7. The activation energy of PANI nanoparticles are decreased
from 47.4 to 36.8 mev with increasing particle sizes from
3.2 to 10 nm. This is due to the shift of the Fermi level in
impurity doped samples.