Synthesis and characterization of conductive polypyrrole/multi-walled carbon
nanotubes composites with improved solubility and conductivity
Tzong-Ming Wu
*
, Hsiang-Ling Chang, Yen-Wen Lin
Department of Materials Science and Engineering, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan
article info
Article history:
Received 16 September 2008
Received in revised form 14 December 2008
Accepted 17 December 2008
Available online 25 December 2008
Keywords:
A. Nano composites
A. Polymers
B. Electrical properties
D. Transmission electron microscopy
Multi-walled carbon nanotubes
abstract
High conductivity and solubility of polypyrrole (PPy)/multi-walled carbon nanotubes (MWCNT) compos-
ites has been successfully synthesized by in situ chemical oxidation polymerization using various con-
centrations of cationic polyelectrolyte poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate
(APS). Raman spectroscopy, FTIR, EPR, FESEM and HRTEM were used to characterize their structure
and morphology. These images of FESEM and HRTEM showed that the fabricated PPy/MWCNT compos-
ites are one-dimensional core-shell structures with the average thickness of the PPy/MWCNT composites
without PSS is about 250 nm and considerably decreases to 100–150 nm by adding the PSS content. The
results of Raman spectrum, FTIR and UV–Vis indicate the synthesized PPy/MWCNT composites are in the
doped state. The conductivities of PPy/MWCNT composites synthesized with the weight ratio of PSS/pyr-
role monomer at 0.5 are about two times of magnitude higher than that of PPy/MWCNT composites with-
out PSS. These results are perhaps due to the part of cationic electrolyte served as a dopant can be
incorporated to the PPy structure to improve the conductivity of fabricated PPy/MWCNT composites.

it is necessary to point out that chemically and electrochemically
synthesized PPy generally contains very poor solubility. It is almost
insoluble in all common organic solvents and in water that re-
stricts its processibility. Many investigations have been made to
enhance the solubility of PPy by designing colloidal forms using
surfactant and the protonation with an organic acid [16–18].Ina
previous report [18], the chemically synthesized PPy doped with
a bulky anion of dodecylbenzenesulfonic acid (DBSA) was soluble
in m-cresol. The conductivity of PPy was about 1 S/cm. After disso-
lution in a polar solvent, the conductivity reduced into 10
À2
S/cm
when cast into a film. Several reports also reveal that the physical
properties of fabricated PPy strongly depend on the types of surfac-
tants/organic acids [19,20]. Nevertheless, conductive PPy with one-
dimensional nanostructure are seldom mentioned among these
reports.
A most effective method of fabricating one-dimensional nano-
structure is using the template-directed synthesis in which reac-
tant materials are located within or in the immediate vicinity of
the templates [21]. Many appropriate nanoscale templates have
been reported, including channels in porous inorganic material
and existing nanowires served as hard templates and block copoly-
mers or self-assembled organic surfactants served as soft tem-
plates [22–24]. CNTs served as hard templates have recently
0266-3538/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.compscitech.2008.12.010
* Corresponding author. Tel.: +886 4 2287 2482; fax: +886 4 2285 7017.
E-mail address: (T M. Wu).
Composites Science and Technology 69 (2009) 639–644

2. Experimental
2.1. Synthesis of PPy/MWCNT composites
2.1.1. Synthesis of PPy
The MWCNTs were prepared by ethylene chemical vapor depo-
sition using Al
2
O
3
supported Fe
2
O
3
catalysts. The diameter of
MWCNT is about 40 nm and the purity of MWCNTs is higher than
90%. Pyrrole monomer (98%, Aldrich Chemical Co.) was purified by
distillation under reduced pressure. Other reagents, including
poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate
(APS), were used without further purification.
The polypyrrole (PPy)/MWCNT composites were synthesized
using in situ chemical oxidative polymerization. In a typical syn-
thesis experiment, various weight ratios of PSS was prepared in
distilled water in a reaction vessel containing a magnetic stirring
bar and the 1 wt% MWCNT was then mixed with the surfactant
solution and ultrasonicated (240 W) over 3 h to form PSS/
MWCNT template in solution. The freshly distilled 0.5 g of pyr-
role monomer was slowly added dropwise into the stirred solu-
tion and continuously stirred for 30 min. The 2.04 g of APS was
first dissolved in 10 ml distilled water and then slowly added
into the solution. Therefore, the polymerization was carried out
for 3 h below 5 °C with constant mechanical stirring. The synthe-

2
) can be determined from
the peak-to-peak linewidth according to
1
T
2
¼
gb
D
H
1=2
h
;
D
H
1=2
¼
ffiffiffi
3
p
D
H
PP
ð1Þ
where b is the Bohr magneton (9.274 Â10
À21
erg G
À1
),
D

quartz cell and deionized water was used as a blank. The peak
position of the Raman, FTIR and UV–Vis spectra was determined
using the peakfit software package. The presented spectrum is
an average of three spectra measured at different regions over
the entire sample range. Thermal stabilities of the resulting
PPy/MWCNT composites were performed from 50 to 800 °Cat
a heating rate of 10 °C/min using a Perkin–Elmer thermogravi-
metric analysis (TGA) and all experiments were operated under
a nitrogen atmosphere at a purge rate of 100 ml/min. All spec-
imens weighed about 6 mg. Linear h/2h X-ray intensity scans of
these specimens were recorded using a Mac MXT III diffractom-
eter with Ni-filtered Cu K
a
radiation in the reflection mode. The
morphology of all samples was characterized by field-emission
scanning electron microscopy (FESEM) and high-resolution
transmission electron microscopy (HRTEM). FESEM measure-
ments were conducted at 3 kV using a JEOL JSM-6700 F field-
emission instrument. HRTEM experiments were performed on
a JEOL JSM-2010 instrument with an accelerating voltage of
200 kV. The samples for HRTEM images were prepared by cast-
ing a drop of the sample suspended in ethanol on a copper grid
covered with carbon.
2.3. Electrical properties
The samples of MWCNT, PPy and PPy/MWCNT composites were
pressed into pellet form under 20 MPa. Furthermore, the conduc-
tivity at room temperature was measured by a programmable DC
voltage/current detector with four probe method. The data shown
here are the mean values of measurements from at least three
samples.

phous PPy layer on the surface of MWCNT can be influenced by
various contents of PSS.
3.2. Physical properties of PPy/MWCNT composites
The molecular structure of the resulting PPy/MWCNT compos-
ites synthesized by cationic polyelectrolyte PSS was characterized
using Raman and IR spectra. Fig. 4 exhibits the Raman spectra of
PPy/MWCNT composites with various concentrations of PSS. All
data demonstrate that the synthesized PPy/MWCNT composites
with the presence of PSS have approximately identical peak posi-
tions associated with the structure of the PPy. The peaks at 935
and 1080 cm
À1
have been attributed to the quinonoid bipolaronic
structure and those at 970 and 1055 cm
À1
with the quinonoid
polaronic structure, exhibiting the presence of the doped PPy
structures [34]. The peak at 1240 cm
À1
is considered to the anti-
symmetrical C–H in-plane bending and the C@C stretching peak
at 1600 cm
À1
is related to be an overlap of the two oxidized struc-
ture. Fig. 5 shows the FTIR spectrum of PPy/MWCNT composites
with various concentrations of PSS. Normally, this spectrum shows
a rich-band fingerprint region, revealing seven strong intensity
bands [35]. All results demonstrate almost the same peak positions
of the main IR bands which are associated with the structure of the
Fig. 1. Vials (6 mL) containing aqueous dispersion of 1 wt% PPy/MWCNT composites synthesized with weight ratio of PSS/pyrrole monomer of (b) 0.1, (c) 0.3 and (d) 0.5. For

in the doped state. The typical absorption peaks of PPy/MWCNT
composites slightly shift to 492 nm as the loading of the weight ra-
tio of cationic electrolyte PSS/pyrrole monomer at 0.1. While the
structure of PPy was continuously doped with high content of
PSS, the absorption peak associated with the polaron-
p
transition
was significantly shifted to a smaller wavelength with increasing
the PSS content. These results exhibit the possible interaction be-
tween the quinoid rings of PPy and SO
2À
4
ion of PSS.
The thermal stability of the PPy/MWCNT composites prepared
in the presence of PSS was studied by TGA analysis. Fig. 7 presents
the curves of weight loss versus temperature of PPy/MWCNT com-
posites with various concentrations of PSS. For comparison, the
TGA analysis of PSS and MWCNT are also shown in this figure.
The first significant weight loss PPy/MWCNT composites which
corresponds to polymer degradation starts at about 200 °C.
Although these curves of PPy/MWCNT composites symthesized
with various concentrations of PSS have the same shape, PPy/
MWCNT composites with high PSS content seems to be slightly
more stable if we compare its TGA curve with the curve of PPy/
MWCNT composites with low PSS content in the whole tempera-
ture range. This data demonstrates that the addition of high ther-
mal stability of PSS is more stable for the all temperature range
of measurement. Clearly, the 10% loss temperature (T
À10%
) of the

presence of high thermal stability PSS and MWCNT.
The electrical conductivities of PPy/MWCNT composites were
measured using the standard four-probe method. The room-tem-
perature conductivities of MWCNT and PPy/MWCNT composites
without PSS were 28.4 and 40 S/cm. In the meantime, the conduc-
tivity of PPy/MWCNT composites with various contents of PSS at
room temperature clearly depends on the contents of PSS. By add-
ing the weight ratio of cationic electrolyte PSS/pyrrole monomer at
0.1, the conductivity at room temperature slightly increases from
40 S/cm to 49 S/cm. With the continuous increase in the loading
of PSS, the conductivities at room temperature continuously in-
crease from 49 Scm for the PPy/MWCNT composites with the
weight ratio of cationic electrolyte PSS/pyrrole monomer at 0.1
to 73 and 91 S/cm for these synthesizd PPy/MWCNT composites
with the weight ratio at 0.3 and 0.5, respectively. It is necessary
to point out that all conductivities of PPy/MWCNT composites pre-
pared with the presence of PSS are in the range between 50 S/cm
and 90 S/cm, which is at least one order in magnitude higher than
those synthesized PPy/MWCNT composites reported in the litera-
tures [37,38]. The conductivities of PPy/MWCNT composites fabri-
cated with the weight ratio of cationic electrolyte PSS/pyrrole
monomer at 0.5 at room temperature are about two times of mag-
nitude higher than that of PPy/MWCNT composites prepared with-
out PSS, perhaps because the part of cationic electrolyte can be
incorporated to the PPy structure served as a dopant to enhance
the conductivity of synthesized PPy/MWCNT composites. Increas-
ing PSS content in these conducting polymers also improves their
conductivities and these results may be due to the decrease in
the thickness of PPy with the presence of high content of PSS.
In order to understand the role of PSS during the formation of

pp
of the PPy with various contents of
PSS were larger than that of the PPy, while the T
2
was reverse [41].
These results reveal that PPy/MWCNT composites with various
contents of PSS has lower polaron mobility, which coincides with
more hydrogen bond between PPy and PSS, while higher polaron
mobility of PPy/MWCNT composites without PSS indicates less
hydrogen bond between PPy and PSS. But the N
S
of the PPy/
MWCNT composite with various contents of PSS were larger than
that of the PPy/MWCNT composite without PSS, indicating an in-
crease in spin concentration for PPy with various contents of PSS.
These results can be assigned to more polaron formation for PPy
with various contents of PSS [42]. Therefore, we can conclude the
conductivity of PPy is dominant by the number of polaron forma-
tion during the in situ polymerization by adding H
+
to the b-posi-
tion of pyrrole ring during the in situ doping polymerization of
pyrrole [37].
4. Conclusions
High-conductivity polypyrrole (PPy)/multi-walled carbon nano-
tubes (MWCNTs) composites with well-dispersion in ethanol has
been successfully synthesized by in situ chemical oxidation poly-
merization using various concentrations of cationic polyelectrolyte
poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate
(APS). These images of FESEM and HRTEM showed that the fabri-

19
49
PPy3/MWCNT 0.3 5.67 2.0025 1.07 5.78 4.30 Â 10
19
73
PPy4/MWCNT 0.5 9.38 2.0024 1.08 3.49 6.06 Â 10
19
91
T M. Wu et al. /Composites Science and Technology 69 (2009) 639–644
643
thesized with the weight ratio of PSS/pyrrole monomer at 0.5 are
about two times of magnitude higher than that of PPy/MWCNT
composites without PSS. These results are perhaps due to the part
of cationic electrolyte served as a dopant can be incorporated to
the PPy structure to improve the conductivity of fabricated PPy/
MWCNT composites.
Acknowledgements
The financial support provided by National Science Council
through the Project NSC96-2212-E-005-049 is greatly appreciated.
References
[1] Iijima S, Ichihashi T. Single-shell carbon nanotubes of l nm diameter. Nature
1993;363:603–5.
[2] Fan S, Chapline MG, Franklin NR, Tombler TW. Self-oriented regular arrays of
carbon nanotubes and their field emission properties. Science
1999;283:512–4.
[3] Dai H, Hafner JH, Rinzler AG, Colbert DT, Smalley RE. Nanotubes as nanoprobes
in scanning probe microscopy. Nature 1996;384:147–50.
[4] Wong EW, Sheehan PE, Lieber CM. Nanobeam mechanics: elasticity,
strength, and toughness of nanorods and nanotubes. Science
1997;277:1971–5.

[17] Omastova M, Trchova M, Pionteck J, Prokes J, Stejskal J. Effect of
polymerization conditions on the properties of polypyrrole prepared in the
presence of sodium bis(2-ethylhexyl) sulfosuccinate. Synth Met
2004;143:153–61.
[18] Lee JY, Kim DY, Kim KJ. Synthesis of soluble polypyrrole of the doped state in
organic solvents. Synth Met 1995;74:103–6.
[19] Kudoh Y, Akami K, Matsuya Y. Properties of chemically prepared polypyrrole
with an aqueous solution containing Fe
2
(SO
4
)
3
, a sulfonic surfactant and a
phenol derivative. Synth Met 1998;95:191–6.
[20] Kupila EL, Kankare J. Influence of electrode pretreatment, counter anions and
additives on the electropolymerization of pyrrole in aqueous solutions. Synth
Met 1995;74:241–9.
[21] Xia YN, Yang PD. Guest editorial: chemistry and physics of nanowires. Adv
Mater 2003;15:351–2.
[22] Nicewarner-Pena SR, Freeman RG, Reiss BD, He L, Pena DJ, Walton ID.
Submicrometer metallic barcodes. Science 2001;294:137–41.
[23] Mayya KS, Gittins DI, Dibaj AM, Caruso F. Nanotubes prepared by templating
sacrificial nickel nanorods. Nano Lett 2001;1:727–30.
[24] Kim F, Song J, Yang P. Photochemical synthesis of gold nanorods. J Am Chem
Soc 2002;124:14316–7.
[25] Ajayan PM, Stephan O, Redlich P, Colliex C. Carbon nanotubes as removable
templates for oxide nanocomposites and nanostructures. Nature
1995;375:564–7.
[26] Zhang Y, Franklin NW, Chen RJ, Dai H. Metal coating on suspended carbon

and pyrrole in the presence of poly(vinylpyrrolidone). J Phys Chem B
2005;109:18283–8.
[37] Sahoo NG, Jung YC, So HH, Cho JW. Polypyrrole coated carbon nanotubes:
synthesis, characterization, and enhanced electrical properties. Synth Met
2007;157:374–9.
[38] Guo H, Zhu H, Lin H, Zhang J. Polypyrrole-multi-walled carbon nanotube
nanocomposites synthesized in oil–water microemulsion. Colloid Polym Sci
2008;286:587–91.
[39] Stucki JW, Banwart WL. Advanced chemical methods for soil and clay mineral
research. Dordrecht: Reidel; 1980.
[40] Jeevananda T, Siddaramaiah S, Seetharamu S, Saravanan S, D’Souza L. Synthesis
and characterization of poly (aniline-co-acrylonitrile) using organic benzoyl
peroxide by inverted emulsion method. Synth Met 2004;140:247–60.
[41] Lin HK, Shih CC, Wang GP, Wu TR, Wu KH, Chang TC. EPR studies of blends of
polyaniline with poly(methyl methacrylate-co-glycidyl methacrylate
iminodiacetic acid). Synth Met 2005;151:256–60.
[42] Luthra V, Singh R, Gupta SK. Mechanism of dc conduction in polyaniline doped
with sulfuric acid. Curr Appl Phys 2003;3:219–22.
644 T M. Wu et al. /Composites Science and Technology 69 (2009) 639–644