1. RESEARCHARTICLE
Copyright © 2009 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol.9, 2169-2172, 2009
Synthesis of Nanoparticles and Nanofibers of Polyaniline
by Potentiodynamic Electrochemical Polymerization
Miguel G. Xavier1 4
, Everaldo C. Venancio1 2 3 ∗
, Ernesto C. Pereira4
, Fabio L. Leite1
,
Edson R. Leite4
, Alan G. MacDiarmid2 †
, and L. H. C. Mattoso1
1
Alan G. MacDiarmid Institute for Innovation and Business and National Nanotechnology Laboratory for Agribusiness (LNNA),
Embrapa Agricultural Instrumentation, C.P. 741, 13560-970, São Carlos-SP, Brazil
2
Department of Chemistry, University of Pennsylvania, 231 South 34th Street, 19104, Philadelphia-PA, USA
3
Centro de Ciências Naturais e Humanas (CCNH), Universidade Federal do ABC, Rua Santa Adélia, 166, Bairro Bangu,
09210-170, Santo André-SP, Brazil
4
Departamento de Química, Universidade Federal de São Carlos, C.P. 676, 13560-905, São Carlos-SP, Brazil
Potentiodynamic electrochemical synthesis was used to controllably synthesize nanofibers (mean
diameter 48 nm) and/or nanoparticles (mean diameter 88 nm) of polyaniline (PANI) on gold elec-
trodes. The films were characterized by cyclic voltammetry (CV), field emission gun scanning elec-
tron microscopy (FEG-SEM) and atomic force microscopy (AFM). The type and dimensions of the
nanostructures depend on deposition conditions such as monomer concentration and scan rate.
This study shows that the nucleation and growth steps play a key role on the film development and
its nano-morphology.
Keywords: Polyaniline, Nanofibers, Nanoparticles, Electrochemical Polymerization,
Nanostructures, AFM, SEM.
Polyaniline (PANI) is a promising conducting polymer
due to its unique physical and chemical properties which
can be used to prepare nanostructures.1–5
One important
feature of these materials is the great dependence of the
polymer morphology, structure and chain size on the syn-
thesis conditions. Chemical polymerization of aniline is
the most usual method to prepare PANI. In the litera-
ture there are many routes proposed to obtain different
morphologies of PANI such as nanotubes6–9
and hollow
microspheres8
through self-assembly method,8–9
ultrasonic
irradiation7
or by changing the molar ratio of the dopant
to monomer.8
Nano and micro spheres were prepared
by aqueous oxidative polymerization of aniline in dif-
ferent solution pH 10
or by changing the hydrophobic-
ity of the substrate where the polymer was deposited.11
Nanoparticles can be obtained changing the solution stir-
ring speed which affects the nucleation12
and also by
the presence of amphiphilic triblock copolymer micelles.13
Kaner et al. described the change of nanofibrilar morpho-
logy of PANI exposing the material to light which gen-
erates heat through non-radioactive energy dissipation and
exothermic photochemical reactions.14–15
Another way to
∗
Author to whom correspondence should be addressed.
†
In Memoriam
produce, nanocomposites of PANI which has been inves-
tigated is by using carbon nanotubes.16–17
A promising approach to obtain PANI nanostructures,
which were less explored in the literature, is the use of
electrochemical procedures. Potentiodynamic electrochem-
ical synthesis is the most used electrochemical technique
which allows the control of several parameters such as
final electrode potential, number of cycles and scan rate,
which might be important to determine the structure of the
polymer produced. In addition, different types of solvents
and electrolytes, i.e., dopants, which can play an impor-
tant role on the definition of polymer morphology, can be
also used. The nanostructures which can be obtained there-
from may open new possibilities for the preparation of
sensors for different liquid analytes (electronic tongue)18–19
or gases.20–21
Considering that small number of studies exploring the
formation of nanostructures based on conventional electro-
chemical synthesis,22–24
in this work we investigated the
electrochemical synthesis of PANI nanoparticles and nano-
fibers using CV, studying the effect of monomer concen-
tration, scan rate and the potential window on the PANI
morphology.
The electropolymerization of aniline was carried out
in the presence of 1.0 mol L−1
HCl aqueous solution.
J. Nanosci. Nanotechnol. 2009, Vol. 9, No. 3 1533-4880/2008/8/001/004 http://dx.doi.org/10.1166/jnn.2009.409 1

2. RESEARCHARTICLE
Synthesis of Nanoparticles and Nanofibers of Polyaniline by Potentiodynamic Electrochemical Polymerization Xavier et al.
A conventional three-electrode electrochemical glass cell
consisting of a platinum foil (counter electrode), saturated
calomel electrode (SCE, reference electrode) and a gold
electrode (working electrode) was used for the potentiody-
namic electrochemical synthesis. The syntheses were per-
formed using a potentiostat/galvanostat Autolab PGSTAT
30 instrument. A potential window from −0.2 V to 1.0 V,
scan rate of 30 mV s−1
or 50 mV s−1
and the aniline con-
centration from 0.02 mol L−1
to 0.5 mol L−1
were used as
described in the results and discussion section. The PANI
films obtained were rinsed with 1.0 mol L−1
HCl aque-
ous solution and then characterized electrochemically in
1.0 mol L−1
HCl aqueous solution. All the experiments
were performed at 25 C.
The PANI nanostructures were evaluated using
FEG-SEM ZEISS model SUPRA 35 and a Discoverer
model TMX 2010 AFM instrument in contact mode,
including special cantilevers of Si3N4 (0.09 N m−1
) tips.
The AFM images were analyzed using WSxM (Nanotec
Electronica S.L.) software.25
The average diameter of the
nanoparticles and nanofibers were analyzed using the free
software ImageJ 1.37 v.26
Figures 1 and 2 present the polymerization of PANI
prepared using different experimental conditions and the
respective MEV and AFM images. In the potentiody-
namic electrochemical synthesis presented in Figures 1(a)
and 2(a), the current peak intensities increase with the
number of cycles, indicating a regular growth of PANI
nanostructures. There are two redox current peaks in
Figure 1(a), peaks A and B. In both Figures 1(a) and 2(a),
the current peak A slightly shifts to more positive poten-
tials as the growth proceeds, which is probably related
to the thickening of PANI films during its polymeriza-
tion. In the literature, this peak potential is proposed to
be related to the radical cation generated upon oxidation
(polaron state).27–28
The current peak A∗
is broader and
more negative compared with current peak A, as expected.
Current peak B shifts to lower potential, which means that
an autocatalytic polymerization occurs during electrolysis
of aniline and diradical cations may be generated, which
are attributed to further oxidation of PANI to its quinoid
form (bipolaron state).29
In Figure 2(a) there are 4 redox processes, i.e., redox
pairs M/M∗
, peak G, and H/H∗
, beside the peaks A/A∗
.
The main difference in the experimental conditions com-
paring Figures 1(a) and 2(a), is the low monomer
concentration and the displacement of the final potential
towards more positive values. A more detailed explana-
tion for the changes in the synthesis voltammograms are
beyond the objectives of the present work, but most impor-
tantly there are significant changes in the polymer mor-
phologies at the nanometer scale, as it will be shown.
The results presented in Figure 2(a) indicates that the gold
electrode surface was not completely coated with nanopar-
ticles of polyaniline, as it can be seen from the current
(a)
(b)
(c)
Fig. 1. (a) Cyclic voltammogram of the aniline polymerization in the
presence of 1.0 mol L−1
HCl aqueous solution containing 0.5 mol L−1
aniline under electrical potential interval of −0.2 V to 1.0 V (8 cycles
and scan rate at 50 mV s−1
); (b) SEM image of PANI nanofibers elec-
tropolymerized (cyclic voltammetry) in the presence of 1.0 mol L−1
HCl
aqueous solution containing 0.5 mol L−1
aniline under potential interval
of −0.2 V to 1.0 V (8 cycles and scan rate at 50 mV s−1
); (c) 3D AFM
images of PANI nanofibers synthesized as described in Figure 1(a). Scan
range of 1 5×1 5 m.
peaks H/H*, which could be related to the gold oxide for-
mation on the exposed gold surface. The current peak G
is related to the monomer electro-oxidation. Concerning
the current peaks M/M∗
, some authors30
have attributed
them to the presence of a polymer containing phenazine
rings, while others28
proposed the oxidation and reduction
2 J. Nanosci. Nanotechnol. 9, 2169-2172, 2009

3. RESEARCHARTICLE
Xavier et al. Synthesis of Nanoparticles and Nanofibers of Polyaniline by Potentiodynamic Electrochemical Polymerization
(a)
(b)
(c)
Fig. 2. (a) Cyclic voltammogram of the aniline polymerization in the
presence of 1.0 mol L−1
HCl aqueous solution containing 0.02 mol L−1
aniline under electrical potential interval of −0.2 V to 1.0 V (first cycle,
scan rate at 30 mV s−1
) and −0.2 V to 0.9 V (the following cycles,
scan rate at 50 mV s−1
); (b) SEM image of PANI nanoparticles elec-
tropolymerized (cyclic voltammetry) in the presence of 1.0 mol L−1
HCl
aqueous solution containing 0.02 mol L−1
aniline under potential interval
of −0.2 V to 1.0 V (first cycle, scan rate at 30 mV s−1
) and −0.2 V
to 0.9 V (the following cycles, scan rate at 50 mV s−1
); (c) 3D AFM
images of PANI nanoparticles synthesized as described in Figure 2(a).
Scan range of 1 5×1 5 m.
of degradation by products. Despite this controversy, it is
well known31–33
that changes on the electropolymerization
conditions leads to changes in the initial nucleation and
growth steps of PANI, which we believe might be dictat-
ing the type and size of the nanostructure that is being
formed.
The electropolymerization condition involves several
different variables, such as potential window, scan rate,
substrate, electrolyte, ionic strength and aniline concen-
tration. Our experimental results indicate that the concen-
tration of aniline plays a key role in the formation of
either nanofibers or nanoparticles, with higher concentra-
tions of aniline (0.5 mol L−1
) promoting a greater the yield
of nanofibers as compared to lower (0.02 mol L−1
ani-
line) where basically only nanoparticles can be obtained,
under the conditions investigated. Using the SEM images
(Figs. 1(b) and 2(b)) and 3D AFM images important
insights from morphology polymer growth can be inferred.
Figure 1(b) shows PANI nanofibers with average diameter
of 48.2 nm. Figure 2(b) shows PANI nanoparticles with
average size of 87.7 nm. Figure 1(c) shows bundles of
PANI nanofibers. Surprisingly, these AFM images show
that, for the first time, the nanofibers are composed of coa-
lescent nanoparticles once the fiber radius has an oscilla-
tory behaviour in the length direction. Figure 2(c) suggests
that the nanoparticles agglomerate into interconnected net-
works until they form branched network-like nanofibers.
Besides, Figure 2(c), which is the image of the same sam-
ple of Figure 2(b), shows a high density region of the
nanoparticles which seems to start such process. Mandic27
proposed that such structures growth in two steps: nucle-
ation onto bare electrode (step 1) followed by the PANI
growth on the already deposited PANI modified surface
(step 2).
Nanoparticles (mean diameter 88 nm) and nanofibers
(mean diameter 48 nm) of polyaniline can be synthe-
sized by electrodeposition using a potentiodynamic elec-
trochemical method. The type, amount and dimensions of
the nanostructures produced depend strongly on the elec-
tropolymerization conditions such as monomer concentra-
tion, scan rate and the electrical potential interval used.
The nucleation process and the growth kinetics are cru-
cial in defining the morphology of the nanostrucutures
obtained. In addition, AFM studies suggest that nanofibers
of PANI seem to be formed by joined nanoparticles.
Acknowledgments: The financial support given by
LABEX-Embrapa, CNPq, FINEP and FAPESP are grate-
fully acknowledged. This paper is in honor of Professor
Alan G. MacDiarmid. It is also the first paper published
by the Alan G. MacDiarmid Institute for Innovation and
Business located at the LNNA, Embrapa/CNPDIA, São
Carlos-SP, Brazil.
References and Notes
1. C. E. Borato, F. L. Leite, L. H. C. Mattoso, R. C. Goy, S. P.
Campana, C. L. de Vasconcelos, C. G. D. T. Neto, M. R. Pereira,
J. L. C. Fonseca, and O. N. Oliveira, IEEE Trans. Diel. Elec. Ins.
13, 1101 (2006).
2. F. L. Leite, L. G. Paterno, C. E. Borato, P. S. P. Herrmann, O. N.
Oliveira, and L. H. C. Mattoso, Polymer 46, 12503 (2005).
J. Nanosci. Nanotechnol. 9, 2169-2172, 2009 3

4. RESEARCHARTICLE
Synthesis of Nanoparticles and Nanofibers of Polyaniline by Potentiodynamic Electrochemical Polymerization Xavier et al.
3. E. C. Venancio, L. G. Paterno, N. Consolin, C. E. Borato,
A. Firmino, and L. H. C. Mattoso, J. Braz. Chem. Soc. 16, 558
(2005).
4. L. G. Paterno and L. H. C. Mattoso, J. Appl. Pol. Sci. 83, 1309
(2002).
5. L. G. Paterno and L. H. C. Mattoso, Polymer 42, 5239 (2001).
6. J. Stejskal, I. Sapurina, M. Trchova, E. N. Konyushenko, and
P. Holler, Polymer 47, 8253 (2006).
7. X. Lu, H. Mao, D. Chao, W. Zhang, and Y. Wei, Macromol. Chem.
Phys. 207, 2142 (2006).
8. L. Zhang and M. Wan, Adv. Funct. Mater. 13, 815 (2003).
9. Z. Zhang, Z. Wei, and M. Wan, Macromolecules 35, 5937 (2002).
10. E. C. Venancio, P. C. Wang, and A. G. MacDiarmid, Synth. Met.
156, 357 (2006).
11. H. J. Ding, C. J. Zhu, Z. M. Zhou, M. Wan, and Y. Wei, Macromol.
Rapid. Comm. 27, 1029 (2006).
12. D. Li and R. B. Kaner, J. Am. Chem. Soc. 128, 968 (2006).
13. D. Cheng, S. C. Ng, and H. S. O. Chan, Thin Solid Films 477, 19
(2005).
14. J. Huang and R. B. Kaner, Chem. Commun. 367 (2006).
15. J. Huang and R. B. Kaner, Nat. Mat. 3, 783 (2004).
16. B. Philip, J. Xie, J. K. Abraham, and V. K. Varadan, Pol. Bull. 53,
127 (2005).
17. G. M. Nascimento, P. Corio, R. W. Novickis, M. L. A. Temperini,
and M. S. Dresselhaus, J. Pol. Sci. A Pol. Chem. 43, 815 (2005).
18. F. R. Simões, L. H. C. Mattoso, and C. M. P. Vaz, Sens. Lett. 4, 319
(2006).
19. A. R. Júnior, A. M. G. Soto, S. V. Mello, S. Boné, D. M. Taylor,
and L. H. C. Mattoso, Synth. Met. 132, 109 (2003).
20. S. Virji, R. B. Kaner, and B. H. Weiller, J. Phys. Chem. B 110,
22266 (2006).
21. S. Virji, J. Huang, R. B. Kaner, and B. H. Weiller, Nano Lett. 4, 491
(2004).
22. A. J. Motheo, J. R. Santos, E. C. Venancio, and L. H. C. Mattoso,
Polymer 39, 6977 (1998).
23. M. Szklarczyk, E. Wierzbinski, K. Bienkowski, and M. Strawski,
Electrochim. Acta 51, 1036 (2005).
24. V. Gupta and N. Miura, Electrochem. Comm. 7, 995 (2005).
25. I. Horcas, R. Fernández, J. M. Gómez-Rodriguez, J. Colchero,
J. Gómez-Herrero, and A. M. Baro, Rev. Sci. Instrum. 78, 013705
(2007).
26. http://rsb.info.nih.gov/ij.
27. Z. Mandic, L. Duic, and F. Kovacicek, Electrochim. Acta 42, 1389
(1997).
28. D. E. Stiwell and S.-M. Park, J. Electrochem. Soc. 135, 2254
(1988).
29. S. Mu and J. Kan, Electrochim. Acta 41, 1593 (1996).
30. E. M. Genies, M. Lapkowski, and J. F. Penneau, J. Electroanal.
Chem. 249, 97 (1988).
31. S. J. Choi and S.-M. Park, J. Electrochem. Soc. 149, E26
(2002).
32. E. C. Venancio, C. A. R. Costa, S. A. S. Machado, and A. J. Motheo,
Electrochem. Comm. 3, 229 (2001).
33. S. Y. Cui and S.-M. Park, Synth. Met. 105, 91 (1999).
Received: 17 December 2007. Accepted: 14 March 2008.
4 J. Nanosci. Nanotechnol. 9, 2169–2172, 2009