POLYMERS FOR ADVANCED TECHNOLOGIES
Polym. Adv. Technol. 2008; 19: 229–236
Published online 5 November 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/pat.1003
Poly (3,4-ethylenedioxythiophene) g-Fe2O3 polymer
composite–super paramagnetic behavior and
variable range hopping 1D conduction
mechanism–synthesis and characterization
Kuldeep Singh, Anil Ohlan, Parveen Saini and S. K. Dhawan*
Polymeric & Soft Materials Section, National Physical Laboratory, New Delhi 110012, India
Received 7 March 2007; Revised 21 August 2007; Accepted 21 August 2007
The present paper reports the preparation of poly (3,4-ethylenedioxythiophene) (PEDOT) ferrimagnetic conducting polymer composite by incorporation of ferrite particles in the polymer matrix
by emulsion polymerization. Synthesis of PEDOT–g-Fe2O3 composite was carried out by chemical
oxidative polymerization of EDOT with ferrite particles in the presence of dodecylbenzenesulfonic
acid (DBSA) that works as dopant as well as surfactant in aqueous medium. The resulting conducting
composite possesses saturation magnetization (Ms) value of 20.56 emu/g with a conductivity of
0.4 ScmS1, which was determined by VSM and four probe technique, respectively. B-H curve reveals
that ferrimagnetic particles of g-Fe2O3 show super-paramagnetic behavior at room temperature
which was also observed in PEDOT–g-Fe2O3 composite. The resulting conducting ferrimagnetic
composite shows microwave absorption loss of 18.7–22.8 dB in the frequency range of 12.4–18 GHz.
Thermogravimetric analysis of the composite revealed that the composite is thermally stable up to
230-C. The characterization of the PEDOT–g-Fe2O3 composite was carried out using XRD and FTIR
spectroscopy. Copyright # 2007 John Wiley & Sons, Ltd.
KEYWORDS: conducting polymers; micelles; composites; PEDOT; ferrimagnetic conducting composites
INTRODUCTION
In last few decades, organic polymers possessing p-conjugated
extended system, with low energy band gap, has attracted the
attention of most of the material scientists, engineers, and
technocrats due to their intrinsically conducting nature in
doped form. Among the conducting polymers, much attention has been paid to polypyrrole, polyaniline, polythiophene
and their derivatives. Only very few low band gap polymers
(Eg < 1.5 eV) with high conductivity are known. Poly(3,4ethylenedioxythiophene) (PEDOT), which is a derivative of
polythiophene, has a moderate band gap.1 Polymerization
of 3,4-ethylenedioxythiophene (EDOT) takes place via 2,5couplings so that polymerization yields a polymer with
fewer defects and thus possesses better properties compared
to its thiophene analogs; due to their unique structural
properties and reaction mechanism it can be easily synthesized by both electrochemical and oxidative redox method.2,3
PEDOT has high transparency in visible regime, excellent
environmental stability, low redox potential, good thermal
stability, and can be doped either n-type or p-type which
*Correspondence to: S. K. Dhawan, Polymeric & Soft Materials
Section, National Physical Laboratory, New Delhi 110012, India.
E-mail: [email protected]
shows moderately high conductivity.4,5 These features of
PEDOT could be exploited in various applications in
electronic devices such as electrode material in rechargeable
polymer batteries,6,7 antistatic coating,8,9 electro chromic
devices,10,11 organic light emitting diodes (OLEDs),12,13 EMI
shielding,14,15 polymeric solar cell.16,17 Polymerization of
EDOT can be carried out by various techniques like dispersion method, suspension method, and emulsion method.
EDOT is partially soluble in water so the rate of polymerization retarded that ultimately decreases the conductivity of
the PEDOT. To solve this problem, many research groups
had reported that conductivity of PEDOT could be improved
by adding suitable organic solvent having high dielectric
constant18 which induces a screening effect between the
positively charged EDOT and negatively charged counter
ion and thus reduces the columbic interaction between the
two and enhances the solubility and rate of polymerization.
To enhance the application of conducting polymer in the
field of EMI shielding, memory devices and radar absorbing
material (RAM material), monomer is polymerized in the
presence of ferrite particles, as ferrites are good absorber of
the electromagnetic radiations.19 In recent years, a lot of
research work has been carried out on ferromagnetic composites of polypyrrole and polyaniline incorporating ferrite particles in the polymer matrix by in situ or ex situ process which
Copyright # 2007 John Wiley & Sons, Ltd.
230
K. Singh et al.
possesses moderate magnetization and conductivity.20–31 But
no work is done on the poly(3,4-ethylenedioxythiophene)ferrite composites. In the present paper, we have synthesized
the PEDOT composite with nano crystalline iron oxide with
the help of the emulsion method in aqueous medium by
using chemical oxidative polymerization using ammonium
peroxydisulfate as an oxidizing agent and DBSA as a dopant
which also work as a surfactant. To overcome the insoluble
nature of EDOT in an aqueous medium, homogenization of
EDOT was carried out in dodecylbenzenesulfonic acid
(DBSA) and subsequently polymerization was carried out.
The resulting ferrimagnetic conducting composite possesses
good magnetization value with moderate conductivity,
which is confirmed by VSM and four probe technique.
EXPERIMENTAL
Materials used
3,4-ethylenedioxythiophene (Bayer AG), ammonium per
sulfate (Merck), DBSA, isopropyl alcohol, FeCl3.6H2O
(Merck), FeCl.2.4.H2O (Merck), and aqueous ammonia
solution are the materials used.
Synthesis of the nano crystalline ferric oxide
The ferric oxide g-Fe2O3 was prepared through the conventional precipitation oxidation method.32 A mixture of
ferric chloride FeCl3.6H2O and ferrous chloride FeCl2.4H2O
in a molar ratio of 2:1 was prepared and the resulting mixture
is precipitated by adding aqueous solution of ammonia drop
by drop with continuous vigorous stirring by maintaining
the pH of the solution up to 11–12. The reaction was stirred
for 3–5 hr at room temperature and brownish black precipitate was formed which was filtered and washed
thoroughly with distilled water. The resulting precipitate
was dried for 24 hr at 1208C. The formation of g-Fe2O3
particles was confirmed by XRD with a crystallite size of
9.17 nm and saturation magnetization (Ms) value was found
to be 69.0 emu/g.
Synthesis of the PEDOT–g-Fe2O3 composite via
micro emulsion oxidative polymerization in
aqueous medium
The synthesis of the PEDOT–g-Fe2O3 composite was carried
out by the micro emulsion polymerization method in
aqueous medium. First a micro-emulsion of g-Fe2O3 and
DBSA is prepared by homogenizing DBSA and g-Fe2O3 in
distilled water, with the homogenizer ART-Miccra D-8
(No-10956) at rpm of 10,500 for 50–60 min. A thick paste of
ferric oxide particles embedded in DBSA was formed in which
an appropriate amount of 3,4-ethylenedioxythiophene, EDOT
(0.1 M) was added and again homogenized for 2–3 hr
resulting in the formation of the micelles of EDOT with
g-Fe2O3. The micelles, so formed, are polymerized below 08C
through chemical oxidization polymerization by using
ammonium per sulfate, (NH4)2S2O8 (0.1 M). The mixture
was stirred for 12–15 hr during which the color of the
solution changes from brown to light blue and then finally to
dark green. The product obtained was demulsified using
equal amount of isopropyl alcohol and the product was
filtered and washed with alcohols and dried at 60–658C. A
Copyright # 2007 John Wiley & Sons, Ltd.
similar synthesis was carried out for PEDOT–DBSA in the
absence of ferrite particles.
Structural characterization
The conductivity of the powder pallet of the sample PEDOT–
g-Fe2O3 composite was measured by the four probe method
using Keithley programmable current source and nanovoltmeter attached to digital temperature controller and APD
Cryo cooler. The magnetic measurements of the ferrite as
well as conducting composites were carried out using the
vibrating sample magnetometer (VSM), Model 7304, Lakeshore Cryotronics Inc. USA. FTIR was carried on Nicolet 5700
and XRD studies were carried out on D8 Advance Bruker
AXS X-ray diffractometer from 2u ¼ 108 to 708 at a scan rate of
0.0258/sec. Thermogravimetric analysis of the polymer and
composites was carried on a Mettler Toledo TGA 851e and
DSC measurement was recorded on DSC 855c. Shielding
measurements were carried out on an Agilent E8362B Vector
Network Analyzer in a microwave range of 12.4–18 GHz
(P-band). Measurements were carried out using 15.8 7.9 6 mm3 copper sample holder connected between the
wave guide flanges of network analyzer. To avoid air gap
the above sample holder is modified with a grove of 1.5 mm
on each side and 3 mm deep.
RESULT AND DISCUSSION
Mechanism
A proper polymerization technique plays a vital role in
determining the morphology, molecular weight, chain
linearity, and internal defects in the properties of the
material. In the PEDOT–g-Fe2O3 composite formation in
the aqueous medium, water is the continuous phase and
DBSA as a surfactant acts as the discontinuous phase and the
monomer EDOT is emulsified along with the ferrite particles
to form micromicelles of oil-in-water type. Emulsion polymerization has high degree of polymerization than those
prepared by suspension and precipitation method. A typical
micelle in an aqueous solution forms a roughly spherical
or globular aggregate with the hydrophilic ‘‘head’’ regions
in contact with surrounding solvent, sequestering the
hydrophobic tail regions in the micelle center. The shape
of a micelle is a function of the molecular geometry of
its surfactant molecules and solution conditions such as
surfactant concentration, temperature, pH, and ionic
strength. Generally in micellar solution there are the chances
of formation of macroscopic particles that can be prevented
by adding the steric stabilizers like poly (vinyl alcohol),
poly (N-vinylpyrrolidone), and cellulose ethers, but in this
present system the bulky surfactant DBSA itself acts to
prevent the formation of the macroscopic precipitation.
When monomer EDOT is added to the DBSA micelle, it
occupies the place in between the micelle and surrounded by
the hydrophilic sulfonate unit and on addition of oxidants
like APS, the polymerization takes place at the interface
boundary. It has also been observed that the color of the
reaction mixture containing DBSA, EDOT, and ferric oxide
changes from dark brown to green before the addition of
oxidant. This color transformation may be due to the
formation of coordination bond between Fe–S of g-Fe2O3
Polym. Adv. Technol. 2008; 19: 229–236
DOI: 10.1002/pat
Poly (3,4-ethylenedioxythiophene) g-Fe2 O3 polymer composite
231
Scheme 1. Proposed mechanism for the polymerization of EDOT.
and monomer EDOT which has a lone pair of electron and
may overlap with the vacant d-orbital of the Fe. This was also
confirmed through FTIR. When the oxidative polymerization
of the micellar solution containing EDOT was carried out by
using the ammonium peroxodisulfate, the color of the
solution starts changing from green to blue and ultimately
to dark black green after the complete polymerization in
12–14 hr. Addition of the APS leads to the formation of
cationic free radicals, which combines with another monomer moiety to form a dimer, which on further oxidation and
combination with another cation radical forms a termer and
ultimately to a long chain of polymer. The polymerization
of the EDOT is shown in Scheme 1 and the proposed
mechanism of coordination of PEDOT with ferric oxide
particles is shown in Scheme 2.
681 cm1. These peaks are almost similar in both blank
PEDOT and PEDOT–g-Fe2O3 composite. FTIR spectra of the
g-Fe2O3 shows the Fe–O bond stretching at 557 cm1 and
632 cm1 respectively The presence of band at 557 cm1 in
the composite clearly shows the presence of g-Fe2O3 in the
composite which was absent in the blank PEDOT–DBSA.
The absence of band at 632 cm1 in the FTIR spectra of the
composite (Fig. 1, curve c) can be assigned to the formation of
linkage between Fe–S. Moreover there is a shift in the
FTIR characterization of PEDOT and
PEDOT–g-Fe2O3 composite
The formation of the linkage between Fe S was further
investigated by the FTIR spectroscopy. Figure 1 shows the
FTIR spectra of pure g-Fe2O3, PEDOT–DBSA and PEDOT–
g-Fe2O3 composite. The vibrational bands at around
1322 cm1 and 1519 cm1 are due to C–C or C –– C stretching
of quinoid structure of thiophene ring and due to ring
stretching of thiophene ring, respectively. Vibrational bands
at 1186 cm1, 1139 cm1, and 1080 cm1 arise due to C–O–C
bond stretching in the ethylene dioxy group. C–S bond in the
thiophene ring is also seen at 975 cm1, 834 cm1, and
Copyright # 2007 John Wiley & Sons, Ltd.
Scheme 2. Proposed coordination of PEDOT–g-Fe2O3
composite. This figure is available in colour online at www.
interscience.wiley.com/journal/pat
Polym. Adv. Technol. 2008; 19: 229–236
DOI: 10.1002/pat
232
K. Singh et al.
Figure 1. FTIR spectra of ferric oxide (a), PEDOT–DBSA (b),
and PEDOT–DBSA-ferric oxide composite (c).
frequency from 681 cm1 to 689 cm1 which is observed due
to C–S bond stretching.
XRD studies
X-ray scattering pattern of the PEDOT–g-Fe2O3 composite
and iron oxide g-Fe2O3 is shown in Fig. 2. The main peaks for
g-Fe2O3 are observed at 2u ¼ 30.288 (d ¼ 2.95 Å), 35.708 (d ¼
2.51 Å), 43.458 (d ¼ 2.08 Å), 53.808 (d ¼ 1.70 Å), 57.448 (d ¼
1.60 Å), 63.058 (d ¼ 1.47 Å) corresponding to the (2 2 0), (3 1 1),
(4 0 0), (4 2 2), (5 1 1), (4 4 0) reflections33 which matches with
the standard XRD pattern of g-Fe2O3 (Powder Diffraction
File, JCPDS No. 39–1346). The peaks present in g-Fe2O3 were
also observed in the PEDOT–g-Fe2O3 composite which
indicates the presence of ferrite particles in the polymer
matrix. The XRD pattern of PEDOT is shown by the broad
peak at 2u ¼ 24.738 (d ¼ 3.60 Å).34 The line broadening of the
peaks in the entire patterns of both g-Fe2O3 particles and
PEDOT–ferrite composite indicates the small dimensions of
the iron oxide particles. The crystallite size of g-Fe2O3
particle can be calculated by line broadening using Scherer’s
formula
where D is the crystallite size for individual peak of the
crystal in angstroms, l the X-ray wavelength, k the shape
factor, u the Bragg angle in degrees, and b is the line
broadening measured by half-height in radians. The value of
k is often assigned a value of 0.89, which depends on several
factors, including the Miller index of the reflecting plane and
the shape of the crystal. The size of g-Fe2O3 particles can be
calculated from the highest intensity peak35 and estimated as
9.17 nm for pure g-Fe2O3 and 10.64 nm for PEDOT–g-Fe2O3
composite. The unit cell parameters are also calculated for
g-Fe2O3 and PEDOT composite using Powder X software.
The powder X-ray pattern shows cubic structure with
a ¼ 8.33 Å for g-Fe2O3 and a ¼ 8.34 Å for PEDOT–g-Fe2O3
composite.
Thermal behavior of PEDOT and
PEDOT–g-Fe2O3 composite
The thermogravimetric analysis of conducting polymer
PEDOT was carried out in the presence and absence of
ferrite particles in order to see the effect of temperature on
the thermal behavior of the polymer. The thermogram of
PEDOT–DBSA (Fig. 3, curve a) shows that polymer is
thermally stable up to the 1828C. A weight loss of 3% is
observed up to 1108C which is most probably due to the loss
of water molecules entrapped in the polymer moiety. From
1828C to 3008C, the loss is 19.3% which can be accorded to the
dedoping of the dopant from the polymer matrix. But from
3008C to 7008C, there is a continuous loss of 40.8%, which
may be due to the degradation of the polymer backbone.
On comparing this thermogram with the thermal behavior
of the composite (Fig. 3, curve b) the thermal stability of the
composite has been found to increase up to 2308C. Initial
weight loss of 4.6% is observed up to 1108C which may be
due to the loss of water molecules entrapped in the polymer
matrix. From 2308C to 3008C, weight loss observed is 3.7%
which is accounted due to the partial leaching of the dopant
from the polymer composite matrix. A weight loss of 30.2% is
observed from 300 to 7008C, which is accounted due to the
degradation of the polymer backbone and the total weight
D ¼ kl=b cos u
Figure 2. XRD data of ferric oxide (a), PEDOT–ferric oxide
composite (b) and PEDOT–DBSA (c). This figure is available
in colour online at www.interscience.wiley.com/journal/pat
Copyright # 2007 John Wiley & Sons, Ltd.
Figure 3. TGA data of PEDOT (curve a), PEDOT–ferric
oxide composite (curve b) at a scan rate of 108C/min
under N2. This figure is available in colour online at www.
interscience.wiley.com/journal/pat
Polym. Adv. Technol. 2008; 19: 229–236
DOI: 10.1002/pat
Poly (3,4-ethylenedioxythiophene) g-Fe2 O3 polymer composite
loss of 41.3% has been observed up to 7008C. This
enhancement in the thermal stability can be accounted due
to some ionic interaction of the g-Fe2O3 with sulfur atom of
the thiophene ring which may form a coordinate bond
between Fe–S as Fe has an incomplete d-orbital to which
sulfur can donate its lone pair of electrons that results in the
enhancement of the thermal stability of the resulting unit.
DSC behavior of PEDOT synthesized in DBSA medium
shows two peak transitions at 1108C and 2208C which may
correspond to the loss of water entrapped in the polymer
matrix and later to the transition taking place corresponding
to the dopant attached to polymeric backbone. This peak
cannot be accounted to be the true glass transition of the
PEDOT–DBSA. However, DSC behavior of the PEDOT–
g-Fe2O3 composite shows the endotherms at 1008C with a
doublet and second at 2808C which may be associated with
greater interaction of dopant–ferric oxide–polymer system.
temperature. The room temperature conductivity of the
composite was recorded, as 0.4 S/cm while that of PEDOT–
DBSA was 0.02 S/cm. Several models have been used to
explain the conductivity behavior in the polymer. According
to Arrhenius law, conductivity variation follows the relation
sðTÞ ¼ s c exp½ðEF EC Þ=KT
Conductivity measurement
The DC conductivity measurement has been carried out
using the compressed pallet of the PEDOT–g-Fe2O3 in the
temperature range of 300–50K. The DC conductivity follows
the semi conducting behavior and is found to decrease with
ð1Þ
where EF is the Fermi energy, EC is the mobility edge, and sc
is the conductivity at the mobility edge. Figure 5 (curve a)
shows the lns versus. T1 plot and its linearity factor is
calculated to be 0.9784 which shows that the Arrhenius
model is not fully applicable for explaining the conductivity mechanism as in the case of normal semiconductors.
Many other models are also established to explain the conductivity variations of conducting polymers but it is
observed that for the low temperature range of 300–1.8K,
the conductivity studies are best studied by VRH (variable
range hopping) model which follows Mott’s equation36–38
Magnetic properties of the composite
Maghemite (g-Fe2O3) is a cubic spinel structure like (AB2O4)
with vacant B site and two distinct sub lattices (A and B in the
spinal structure) which give origin to ferrimagnetic ordering
in the compound. These nano crystalline g-Fe2O3 particles
show super paramagnetic (SPM) behavior at room temperature with Ms value of 69.0 emu/g (Fig. 4, curve a). When
these particles are incorporated in the polymer matrix
resulting in the formation of PEDOT–g-Fe2O3 composite, the
magnetization value was found to be 20.56 emu/g (Fig. 4,
curve b) while the SPM nature remains unaffected as the
coercivity (Hc ¼ 4.93 G) and retentivity (Mr ¼ 0.1196 emu/g)
remain almost same. From these results it is clear that the
PEDOT–g-Fe2O3 composite is ferrimagnetic in nature and
will work as a good absorber of the microwave in the
GHz range.
233
sðTÞ ¼ s o exp½ðTo =TÞ1=g ð2Þ
where T0 is the Mott characteristic temperature and can be
expressed as
To ¼ 8a=kB NðEF ÞZ
ð3Þ
and sO is the conductivity at T ¼ 1
R ¼ ½ap=KB TNðEF Þ1=2
ð4Þ
1
where a is the localization length which can be determined
from the magneto conductance data. From the observed
values of T0 and so, one can calculate N(EF) density of states,
R, the average hopping distance with the use of Equations (3)
and (4). Exponent g in Equation (2) is the dimensionality
factor having values 2, 3, and 4 for 1-dimension, 2-dimensions,
and 3-dimension conduction mechanism, respectively. In this
paper, lns versus temperature with different values of g as 2,
3, and 4 have been plotted as shown in Fig. 5 (curves b, c, and
d). It is observed that the conductivity data fit for the
one-dimensional VRH model with g ¼ 2 with a linearity
factor of 0.99957 as compared to the linearity factors of 0.9985
and 0.9966 for two and three-dimensional hoping conduction, respectively. From the plots, the calculated value of so is
7.06 S/cm and To is 2438.4 K. Thus from the above data, it
was observed that 1D-VRH model is suitable for the
conduction mechanism of the PEDOT–g-Fe2O3 composite.
Microwave studies in P-Band (12.4–18 GHz)
Shielding effectiveness of a material is defined as the ratio of
transmitted power to incident power, hence for SE measured
in decibel (dB) it is given by
SE ¼ 10 log Pi=Pt
ð5Þ
where Pi (Ei) and Pt (Et) are the power (electric field) of
incident and transmitted EM waves, respectively. For a
single layer of shielding material, the SE is the sum of
contribution due to reflection (SER), absorption (SEA)and
multiple reflection (SEM) and can be given by
SE ¼ SER þ SEA þ SEM ðdBÞ
Figure 4. VSM data of ferric oxide (curve a) and PEDOT–
ferric oxide (curve b).This figure is available in colour online at
www.interscience.wiley.com/journal/pat
Copyright # 2007 John Wiley & Sons, Ltd.
ð6Þ
The S11 or (S22) and S12 or (S21) parameters of the two-port
network system represent the reflection and transmission
coefficients, respectively. According to the analysis of
Polym. Adv. Technol. 2008; 19: 229–236
DOI: 10.1002/pat
234
K. Singh et al.
Figure 5. Variation of conductivity with respect to temperature; plot of lns versus T1 (curve a), lns versus
T1/2 (curve b), lns versus T1/3 (curve c) and lns versus T1/4 (curve d).
S parameters, transmittance (T), reflectance (R), and
absorbance (A) through the shielding material can be
described as
T ¼ jS12 j2 ¼jS21 j2
ð7Þ
R ¼ jS11 j2 ¼jS22 j2
ð8Þ
A¼1RT
ð9Þ
PEDOT–DBSA are 1.63 dB and 8.41 dB at 15.2 GHz respectively, while in the case of PEDOT–g-Fe2O3 composite the
calculated values of SER and SEA are 3.82 dB and 20.7 dB,
respectively. These results suggest that the microwave
Here, it is noted that A is given with respect to the power of
the incident EM wave. If the effect of multiple reflection
between both interfaces of the material is negligible, the
relative intensity of the effectively incident EM wave inside
the materials after reflection is based on the quantity as 1 R.
Therefore, the effective absorbance (Aeff) can be described as
Aeff ¼ (1 R T)/(1 R) with respect to the power of the
effectively incident EM wave inside the shielding material. It
is convenient that reflectance and effective absorbance are
expressed as the form of 10 log (1 R) and 10 log (1 Aeff)
in decibel (dB),39 respectively, which provide the SEA as
follows:
SER ¼ 10 logð1 RÞ
ð10Þ
SEA ¼ 10 logð1 Aeff Þ ¼ 10 logðT=1 RÞ
ð11Þ
Figure 6 shows the measured EMI SEs of the PEDOT–DBSA
and the PEDOT–g-Fe2O3 composite in the 12.4–18 GHz range.
The SER and SEA values calculated by Equations 10 and 11 for
Copyright # 2007 John Wiley & Sons, Ltd.
Figure 6. Variation of shielding effectiveness due to absorption (SEAeff) and shielding effectiveness due to reflectance
(SER) with frequency in P-band (12.4–18 GHz) of PEDOT and
PEDOT–ferrite composite. This figure is available in colour
online at www.interscience.wiley.com/journal/pat
Polym. Adv. Technol. 2008; 19: 229–236
DOI: 10.1002/pat
Poly (3,4-ethylenedioxythiophene) g-Fe2 O3 polymer composite
absorption loss of the PEDOT–g-Fe2O3 composite is better
than the PEDOT polymer which can find its applications as a
futuristic microwave absorbing material.
CONCLUSIONS
The composite PEDOT–g-Fe2O3 synthesized by the emulsion
polymerization has shown ferrimagnetic behavior having a
magnetization value of 20.56 emu/g and moderate conductivity of 0.4 S/cm following the 1D-VRH model with
enhanced thermal stability than PEDOT–DBSA synthesized
without g-Fe2O3. The enhancement in the thermal behavior
of the composite is due to some complex formation between
Fe and S of the thiophene ring. The conducting PEDOT–
g-Fe2O3 composite possessing moderate conductivity with
magnetic behavior can be used in many applications, e.g., in
the field of shielding of electronic equipments from
electromagnetic pollution in the microwave range. Our further studies are concentrating on developing conducting
ferrite coatings which can be used as a protective sheath
coating suitable for RAM applications.
Acknowledgments
The authors express their thanks to Dr. Harikishan for
recording the conductivity data and Dr. R.K. Kotnala for
doing the magnetization measurements of the samples.
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