Preparation and Characterization of Nanocomposite Based on Polyaniline and Graphene Nanosheets
Polymer nanocomposites based on polyaniline (PANi) and graphene nanosheets (GNS) modified with poly(sodium 4-styrensulfonate) (PSS-GNS) were prepared, and their structure and properties were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy, ATR-IR spectros-copy, X-ray diffraction, elemental analysis, thermogravimetric analysis (TGA) and electrical conductivity measure-ments. The results revealed that for the PANi/PSS-GNS nanocomposites, the disordered structure of PSS-GNS was fully destroyed and PSS-GNS exists in the form of a single GNS or stacked PSS-GNS elements in a PANi matrix. PSS-GNS was partly covered by PANi due to hydrogen bonding that occurs between the PSS-GNS and PANi. By incorporating PSS-GNS, the electrical conductivity of PANi increased linearly from 0.84 S/cm for neat PANi to 4.96 S/cm for a PANi/PSS-GNS (5%) nanocomposite. The thermal stability of the PANi was also improved significantly to approximately 100 o C by the nanocomposite.
Macromolecular Research, Vol. 19, No. 2, pp 203-208 (2011) www.springer.com/13233
The Polymer Society of Korea
Preparation and Characterization of Nanocomposite Based on Polyaniline
and Graphene Nanosheets
Ngo Trinh Tung1,3, Tran Van Khai2, Minhee Jeon1, Yeo Jin Lee1, Hoeil Chung1, Jeong-Hwan Bang4,
and Daewon Sohn*,1
1Department of Chemistry, Hanyang University, Seoul 133-791, Korea
2Division of Advanced Materials Science Engineering, Hanyang University, Seoul 133-791, Korea
3Institute of Chemistry, Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Caugiay, Hanoi, Vietnam
4Department of Environmental Health, Seonam University, Namwon 590-711, Korea
Received September 17, 2010; Revised October 20, 2010; Accepted October 30, 2010
Abstract: Polymer nanocomposites based on polyaniline (PANi) and graphene nanosheets (GNS) modified with
poly(sodium 4-styrensulfonate) (PSS-GNS) were prepared, and their structure and properties were investigated by
atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy, ATR-IR spectros-
copy, X-ray diffraction, elemental analysis, thermogravimetric analysis (TGA) and electrical conductivity measure-
ments. The results revealed that for the PANi/PSS-GNS nanocomposites, the disordered structure of PSS-GNS was
fully destroyed and PSS-GNS exists in the form of a single GNS or stacked PSS-GNS elements in a PANi matrix.
PSS-GNS was partly covered by PANi due to hydrogen bonding that occurs between the PSS-GNS and PANi. By
incorporating PSS-GNS, the electrical conductivity of PANi increased linearly from 0.84 S/cm for neat PANi to 4.96
S/cm for a PANi/PSS-GNS (5%) nanocomposite. The thermal stability of the PANi was also improved significantly
to approximately 100 oC by the nanocomposite.
Keywords: polyaniline, graphene nanosheet, conductivity, poly(sodium 4-styrensulfonate).
Intrinsically conducting polymers (ICPs) are promising
materials for applications in electronics, electrochemistry,
electroluminescence, membranes and sensors.1,2 Among the
ICPs, polyaniline (PANi) has attracted considerable atten-
tion because of its easy synthesis, low monomer cost, good
environmental and thermal stability as well as adequate
electrical conductivity.3,4 To improve the properties of PANi,
especially the electrical conductivity, several conductive
nanofillers including gold nanoparticles,5,6 silver nanoparticles7
or carbon nanotubes8 (CNTs) have been used for prepara-
tion of PANi nanocomposites.
In recent years, graphene nanosheets (GNSs) consisting
of one to a few graphene layers have been recognized as a
promising, cost effective and high quality alternative to CNTs
and carbon nanofibers in composite applications. GNSs
exhibit outstanding electrical and thermal conductivity compa-
rable to CNTs, while the specific surface area is twice that
GNS are mostly prepared by physical methods such as
micro-mechanical cleavage of graphite11 or by chemical
reduction of exfoliated graphene oxide nanosheets.12,13 Among
these methods, preparation of GNS from exfoliated
graphene oxide nanosheets has attracted much research
interest because this method is efficient and results in high
yields of single-layered graphene oxide. The main draw-
back of this method is that the graphene oxide nanosheets
contain several oxygen functional groups, including hydroxyl,
epoxy, carbonyl and carboxyl groups, that make graphite
oxide nanosheets strong hydrophilic characters and electri-
cally insulating.14 Therefore, to make graphene oxide
nanosheets electrically active again, graphene oxide
nanosheets must be reduced in order to remove the oxygen
containing moieties and thus, to restore the graphitic struc-
ture. To date, the reduction of graphene oxide nanosheets is
performed by pyrolysis at high temperatures15 or by chemi-
cal treatment using hydrazine, sodium borohydride, or hyd-
roquinone as reducers.13,14
In practice, the reduction of graphene oxide nanosheets
form GNSs results in a decrease in their hydrophilicity, which
eventually leads to their irreversible agglomeration and pre-
cipitation.14 Thus, the hydrophobic character of GNSs can
affect the dispersion of GNSs in a polymer matrix during in
situ polymerization in aqueous solution. The better the
homogeneity is, the better the properties of the composites
*Corresponding Author. E-mail: email@example.com
N. T. Tung et al.
204 Macromol. Res., Vol. 19, No. 2, 2011
such as the electrical conductivity.16 Studies on the prepara-
tion of stable aqueous dispersions of GNSs in the presence
of anionic polymers have been reported.17,18 So far, polymer
nanocomposites based on PANi and pristine graphite,19
graphite oxide20,21 as well as GNSs22 have been investigated.
However, to our knowledge, the modification of GNSs, espe-
cially non-covalent modification, for applications in PANi
based nanocomposite is still limited.
In this paper, polymer nanocomposites based on poly-
aniline and water soluble GNS were prepared and character-
ized. The water soluble GNSs were prepared by reduction
of graphene oxide nanosheets with hydrazine and simulta-
neous modification with poly(sodium 4-styrenesulfonate)
(PSS). The polymer nanocomposites were prepared by in
situ oxidative polymerization of aniline monomer with PSS-
GNS in an acidic aqueous solution. The structure and prop-
erties of the polymer nanocomposites are investigated and
Materials. Aniline (99.5%), nitric acid (70%), potassium
chlorate (99%), poly(sodium 4-styrenesulfonate)(PSS) (99%),
hydrazine hydrate (N2H4:50-60%) and natural graphite
flakes with average diameter of 400 µm were purchased
from Aldrich. Ammonium persulfate (APS) (98%), hydro-
chloric acid (37%) and sulfuric acid (97%) were purchased
from SAMCHUN Chemical. All chemicals were used as
Preparation and Modification of Graphene Nanosheets.
Graphene oxide nanosheets were prepared according to the
Staudenmaier method.23 A reaction flask was charged with
10 mL H2SO4 and 5 mL HNO3 and cooled by immersion in
an ice bath. After stirring and cooling for 15 min, 0.5 g nat-
ural graphite flakes were added under vigorous stirring.
Then, 6 g KClO3 was slowly added to the reaction mixture
and allowed to stir for 5 days. On completion of the reac-
tion, the mixture was filtered and washed several times with
a 5% solution of HCl to remove all sulfate ions, followed by
washing with distilled water. The acid intercalated graphite
flakes were dried at 100 oC for 24 h. The thermal treatment
was performed in a furnace at a temperature of 1,050 oC for
40 sec. Afterward, the worm-like expanded graphite flakes
were sonicated in an ethanol solution (ethanol : water = 2 :
1, v/v) for 10 h. The graphene oxide nanosheets were obtained
after filtering and washing the products with distilled water
and drying in a vacuum oven for 24 h.
To prepare water soluble GNSs, graphene oxide nanosheets
were reduced by hydrazine and simultaneously modified
with PSS according to the procedure suggested by
Stankovich17 et al.. Graphene oxide nanosheets (0.05 g) and
0.5 g PPS were added to a reaction flask containing 50 mL
distilled water. After sonication for 1 h, 3 mL hydrazine
hydrate was added to the mixture. The reaction mixture was
stirred at a temperature of 100 oC under a water-cooled con-
denser for 24 h. PSS modified GNSs were filtered and
washed with distilled water and ethanol and dried in vac-
uum oven at room temperature for 24 h.
Synthesis of PANi/PSS-GNS Nanocomposites. PANi /
PSS-GNS nanocomposites were prepared by in situ poly-
merization of aniline monomer in the presence of PSS-
GNS. In a typical experiment, PSS-GNSs were dispersed in
5 mL ethanol solution (ethanol : water = 3 : 2, v/v) and then
sonicated for 1 h. This suspension was added to a reaction
flask containing 25 mL 1 M HCl solution and 0.9313 g
aniline. The mixture was stirred for 30 min and then 25 mL
1 M HCl solution containing 1.14 g APS was added drop-
wise to the mixture. The reaction mixture was kept under
static conditions for 6 h at 0-5 oC. After the reaction, the
product was filtered, washed with distilled water followed
by ethanol and dried in a vacuum oven at 50 oC for 6 h.
Characterization. The surface topological measurement
of GNS was performed under ambient conditions with
atomic force microscopy (AFM) (XE-100 microscopy, Park
System Corp). The morphology of PANi/PSS-GNS nano-
composites was observed by scanning electron microscopy
(SEM) (JEOL, JSM-840A). XRD experiments were per-
formed on a Bruker-AXS D8 instrument with Cu K
= 1.5406 Å) at 40 kV and 40 mA. ATR-FTIR spectra
were collected on a FTIR spectrometer equipped with a
microscope (SensIR Technologies, Danbury, CT). UV-vis
absorption spectra of the samples were recorded on an Agi-
lent 8453 instrument at ambient temperature. TGA experi-
ments were performed on a TGA-SDT 2960 instrument in
the temperature range from 25 to 800 oC with a heating rate
of 10 oC/min in a N2 atmosphere. Oxygen content in the
sample was determined using an elemental analyzer (Flash
EA 1112 series/CE Instrument). For the characterization of
the electrical conductivity of the materials, the PANi/GNS-
PSS composite powders were pressed into pellets at high
pressure (7.5 ton/cm2, 30 sec) with a thickness of around
300 µm and diameter of 13 mm. In the case of graphene
oxide nanosheets, GNS and PSS-GNS, a film of these mate-
rials on a glass substrate was prepared by a dip-coating
method in ethanol solution (0.001 g/mL). The thickness of
the film was about 2.1 µm. The electrical conductivity of
the samples was measured using the four probe method on a
CMT-Series, Jandel instrument at room temperature.
Results and Discussion
Characterization of PSS Modified GNS. For the prepa-
ration of graphene oxide nanosheets, a thickness in the
range of a single graphene layer is desirable. Figure 1 shows
AFM images of graphene oxide nanosheets on a Si-wafer
after the exfoliation process. It is clear that the obtained
graphene oxide nanosheet has a thickness of around 3~4
nm. Assuming that the thickness of a single graphene layer
Preparation and Characterization of Nanocomposite Based on Polyaniline and Graphene Nanosheets
Macromol. Res., Vol. 19, No. 2, 2011 205
is equal to the interlayer separation in graphite,17,24 0.34 nm,
the obtained graphene oxide nanosheets likely consist of
about 10 graphene layers.
The preparation and modification of GNS was performed
by reduction of graphene oxide nanosheets with hydrazine
in aqueous solution and simultaneously modification by
non-covalent coating with PSS molecules through the
stacking of aromatic molecules on the graphene plane.25,26
To prove the existence of non-covalent interactions between
GNS and PSS, aqueous solutions of GNS, PSS and PSS-
GNS (0.001 g/5 mL) were prepared and filtered through a
PTFE syringe membrane filter (0.45 µm pore size) and sub-
sequently the UV-vis spectra were recorded (Figure 2).
PPS has two absorption peaks at 225 and 261 nm and
GNS has no absorption peaks. After modification with PSS,
two absorption peaks appear at 228 and 282 nm for PSS-
GNS. This result clearly indicates that the PSS molecules
are successfully attached on the surface of GNS. The effect
of coating GNS by PSS molecules is evident by the stability
of the dispersion of GNS with and without PSS in aqueous
solution for long times (about 1 month) (Figure 3).
Meanwhile, the dispersion of PSS-GNS in water, pre-
pared by precipitating GNS in an aqueous solution, is still
stable. According to Stankovich17 et al., the surface of GNS
was partially covered with polymer due to defects in the
graphitic structure of GNS.
Analysis of the Microstructure and Morphology of
PANi/PSS-GNS Nanocomposite. Figure 4 shows the XRD
patterns of pristine graphite, PSS-GNS, PANi and PANi/
PSS-GNS (5%) nanocomposites. Pristine graphite has a
very strong sharp peak at 26.6o, corresponding to the d-
spacing between single graphene layers (0.34 nm). For PSS-
GNS, the strong sharp peak of pristine graphite disappeared
and a broad peak was observed at 23.4o. This XRD pattern
of PSS-GNS is typical for disordered (turbostatic) graphitic
platelets reported by Dresslhaus27 et al.. This result confirms
the successful exfoliation of pristine graphite into graphene
nanosheets. The as-prepared PANi has a semi-crystalline
structure. The main peaks in the PANi XRD pattern are
located at 8.9, 15.0, 20.7, and 25.2o, which correspond to the
Figure 1. A non-contact mode AFM image of graphene oxide nanosheets with height profile.
Figure 2. Comparison of UV-vis spectra of GNS, PSS, and GNS
modified with PSS.
Figure 3. Images of water dispersion (0.001 g/mL) of GNS and
PSS-GNS after 1 month.
N. T. Tung et al.
206 Macromol. Res., Vol. 19, No. 2, 2011
(001), (010), (100), and (110) reflection crystal planes. This
crystal structure of PANi is of the ES-I crystalline type reported
by Pouget28 et al.. For the PANi/PSS-GNS nanocomposite,
it is interesting to see that the reflection peak of PSS-GNS at
23.4o totally disappeared and the XRD pattern of the nano-
composite is almost identical to PANi. This result indicates
that by in situ polymerization of aniline monomer with
PSS-GNS, the disordered structure of PSS-GNS was fully
destroyed and PSS-GNS was exfoliated in the PANi matrix.
Figure 5 shows the SEM-images of PANi and PANi/PSS-
GNS (1%) nanocomposites. It is clear that PANi, that a rod-
like morphology was formed, with diameters from 100 to
170 nm. In the polymer nanocomposite, the rod-like mor-
phology of the neat PANi is less visible. Rather, a particle-
like morphology was formed, and PANi is partly attached
onto the surface of PSS-GNS. It is well known that, when
HCl is used as a dopant, the aniline monomer was absorbed
onto the surface of GNS through electrostatic attraction by
the formation of weak charge-transfer complexes between
aniline monomer and the graphitic structure of GNSs. As
result of the absorption process, GNSs were coated by PANi
particles by the in situ polymerization of aniline monomer
in the presence of GNS.21 In our case, GNSs were partly
covered by PSS molecules. Thus, the PSS molecules pre-
vented the absorption of aniline monomer onto the surface
of GNSs, resulting in partial attachment of PANi on the sur-
face of PSS-GNSs. Based on SEM images, it is clear to see
that PSS-GNSs can exist as a single PSS-GNS or as a stack
of several PSS-GNSs in a PANi matrix.
Analysis of ATR-FTIR Spectra of PANi/PSS-GNS Nano-
composites. Figure 6 shows the typical ATR-FTIR spectra
of PSS-GNS, PANi, and PANi/PSS-GNS (1%) nanocom-
posites. For PSS-GNS, the ATR-FTIR spectrum is domi-
nated by a sharp peak at 1242 cm-1, which is assigned to C-
O-C stretching.18 A less intense, broad peak at 1470 and
1665 cm-1 can be assigned to the C-OH and C=O in carbox-
ylic and carbonyl moieties.18 This result indicates that a
large numbers of epoxy groups were formed on the graphitic
plane by the preparation of GNSs with chemical oxidation
of graphite, PSS,29 with characteristic peaks of S=O stretch-
ing at 1050 and 1030 cm-1 and S-O at 895 cm-1 appear as a
weak broad peak at about at 1050 cm-1. PANi30 has the char-
acteristic peaks of quinoid ring stretching at 1630 cm-1, ben-
zenoid ring stretching at 1512 cm-1, C-N stretching at
1347 cm-1, N=Q=N, (Q is a quinoid) at 1191 cm-1 and C-H
out of plane bending at 825 cm-1. For the PANi/PSS-GNS
nanocomposite, the ATR-FTIR spectrum is almost the same
as the PANi spectrum, except a new peak, which appears at
1376 cm-1 and the C-H bending peak shifted to a higher
wavenumber (846 cm-1). Both PANi and PSS-GNS do not
have any characteristic peaks at 1376 cm-1, and the peak of
C-O-C stretching of PSS-GNS is missing. Therefore, it is
believed that the new peak at 1376 cm-1 in the PANi/PSS-
GNS nanocomposite is a result of shifting of the C-O-C
bonding peak to a higher wavenumber. According to Levitt31
et al., the aromatic ring can act as a hydrogen bond acceptor.
Figure 4. Comparison of XRD patterns of (a) pristine graphite,
(b) PSS-GNS, (c) PANi, and (d) PANi/PSS-GNS (5%) nanocom-
Figure 5. SEM-images of (a) PANi and (b) PANi/PSS-GNS (1%)
Figure 6. ATR-FTIR spectra of PANi, PANi/PSS-GNS (1%)
nanocomposite and PSSGNS.
Preparation and Characterization of Nanocomposite Based on Polyaniline and Graphene Nanosheets
Macromol. Res., Vol. 19, No. 2, 2011 207
Thus, the shifting of both C-O-C bonding in PSS-GNSs and
C-H bending in PANi to higher wavenumber in the nano-
composite clearly indicates that hydrogen bonding exists
between oxygen atoms in the epoxy group of PSS-GNSs
and hydrogen atoms of aromatic rings of PANi.
Electrical Conductivity. Electrical conductivity is one of
the most important properties of composites for applications
in optoelectronic devices. The electrical conductivity of
PANi/PSS-GNS nanocomposites as a function of PSS-GNS
content is shown in Figure 7. It is clear to see that, with
increasing PSS-GNS content, the electrical conductivity of
PANi/PSS-GNS nanocomposites strongly increases from
0.84 S/cm for neat PANi to 4.96 S/cm for the PANi/PSS-
GNS (5%) nanocomposite. Errors in the electrical conduc-
tivity values were about 3%. Graphene oxide nanosheets
containing oxygen moieties have very low electrical con-
ductivity, about 1.7×10-7 S/cm. According to the results of
elemental analysis, the oxygen content in graphene oxide
nanosheets decreases from 8.88% (± 0.17) to 7.18% (± 0.02)
after reduction with hydrazine in aqueous solution. The
removal of the oxygen moieties resulted in an increasing in
electrical conductivity of GNS to 0.3 S/cm, about 6 orders
of magnitude better than the electrical conductivity of
graphene oxide nanosheets. This electrical conductivity of
GNS is close to the electrical conductivity of reduced
graphene oxide (0.24 S/cm) reported by Stankovich14 et al..
After modification of GNS with PSS, the electrical conduc-
tivity of PSS-GNS slightly decreases to 0.14 S/cm. Accord-
ing to Du21 et al. in PANi/PSS-GNS nanocomposites, PSS-
GNS could serve as an electrically conductive bridge in the
PANi matrix, and thus increases the electrical conductivity
of the polymer nanocomposite. At high PSS-GNS content
(more than 3%), a strong increase in the electrical conduc-
tivity of PANi/PSS-GNS nanocomposite was observed. It is
possible that at high PSS-GNS content, a conductive net-
work of PSS-GNS formed, resulting in the strong increase
in electrical conductivity in the nanocomposite.
Thermal Stability. Figure 8 shows the TGA thermo-
grams of PANi, PSS-GNS and PANi/PSS-GNS nanocom-
posites with different PSS-GNS content. PSS-GNSs do not
show any significant weight loss in the temperature range
except weight loss below 100 oC from the moisture absorbed
in the sample. Three weight loss steps are observed in PANi.
The first weight loss below 100 oC is from moisture absorbed
in the sample. The second weight loss from 170 to 270oC is
due to the weight loss of the dopant. Finally, the polymer
begins thermally to degrade at a temperature of 360 oC. The
thermal behavior of the doped PANi is the same as that
reported by Bhadra32 et al.. For the PANi/PSS-GNS nano-
composite, three weight loss steps are also observed. The
first two weight loss steps are identical to neat PANi. The
main difference lies in the weight loss step of the polymer.
In the nanocomposite the degradation temperature of PANi
is significantly increased from 360oC in neat PANi to
460 oC. Further, the thermal behavior of PANi/PSS-GNS
nanocomposite with 5% PSS-GNS is similar to that of pris-
tine PSS-GNS. This result clearly indicates that the thermal
stability of PANi is strongly improved by incorporation of
In this paper, PANi/PSS-GNS nanocomposites were pre-
pared and characterized. By the in situ polymerization pro-
cess, the disordered structure of PSS-GNS was fully destroyed
and both single PSS-GNS and stacked PSS-GNS were dis-
persed in a PANi matrix. Interaction occurs between PANi
Figure 7. Dependence of the electrical conductivity of PANi/
PSS-GNS nanocomposite on the PSS-GNS content.
Figure 8. TGA thermograms of PANi, PSS-GNS, and PANi/
PSS-GNS nanocomposite prepared with different PSS-GNS
contents (the numbers in the figure indicate the content of PSS-
GNS in the nanocomposite in %, w/w).
N. T. Tung et al.
208 Macromol. Res., Vol. 19, No. 2, 2011
and PSS-GNS through hydrogen bonding between the
epoxy group in PSS-GNS and the aromatic ring of PANi.
By the incorporation of PSS-GNS, the electrical conductiv-
ity of PANi strongly increased from 0.84 S/cm in neat PANi
to 4.96 S/cm in PANi/ PSS-GNS nanocomposite with 5%
PSS-GNS. The thermal stability of PANi was also signifi-
cantly improved from 360 oC in neat PANi to 460 oC in
PANi/PSS-GNS nanocomposites. These intriguing features
of the nanocomposites make them promising materials for
applications in electronic devices.
Acknowledgements. This work was supported by a research
fund from Hanyang University.
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