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Materials Chemistry and Physics 112 (2008) 651–658

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

ielectric and magnetic properties of conducting ferromagneticomposite of polyaniline with �-Fe2O3 nanoparticles

uldeep Singha, Anil Ohlana, R.K. Kotnalab, A.K. Bakhshic, S.K. Dhawana,∗

Polymeric & Soft Materials Section, National Physical Laboratory, New Delhi 110012, IndiaMagnetic Standards, National Physical Laboratory, New Delhi 110012, IndiaDepartment of Chemistry, University of Delhi, Delhi 110007, India

r t i c l e i n f o

rticle history:eceived 22 February 2008eceived in revised form 1 May 2008ccepted 8 June 2008

eywords:lectrochemical techniqueagnetic Materialsielectric properties

a b s t r a c t

The present paper reports the synthesis of conducting polyaniline polymer composite with nanoclus-ters of ferrite (�-Fe2O3) particles in the presence of dodecylbenzene sulfonic acid in aqueous mediumthrough electrochemical and chemical oxidative polymerization. Different formulations have been pre-pared to study the effect of ferrite constituent on the electrical and dielectric properties of polyanilinenano-composite. Vibrating sample magnetometer (VSM) studies and electrical conductivity measure-ments have revealed that conducting polymer composite has a saturation magnetization (Ms) value of48.9 emu g−1 and conductivity of the order of 0.13 S cm−1. The particle size of �-Fe2O3 was found in therange of 8–15 nm as analyzed by transmission electron microscopy (TEM). Fourier transform infraredspectroscopy (FTIR) results have shown the presence of characteristic band stretching of Fe O band at

lectrical conductivity630 and 558 cm−1, indicating the presence of �-Fe2O3 in the polyaniline matrix which is in agreement withthe electrochemical results. Dielectric measurements have shown decreasing trend of dielectric constantwith the increase of �-Fe2O3 particles in the polymer matrix while shielding effective (SE) of −11.2 dBwas achieved for the polymer composite in 8.2–12.4 GHz (X-band) frequency range. The characterizationof the composite was further carried out by X-ray diffraction, UV–vis and thermal gravimetric analysis

fdtnmtmccerm

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(TGA).

. Introduction

Electronically conducting polymers are the novel class ofynthetic metals with wide spread application in number ofechnological devices like EMI shielding and electrostatic chargeissipation [1–5], sensors [6–8], organic light emitting diodes9–11] and polymer solar cells [12,13]. The prospects of con-ucting organic magnetic materials have inspired much interesthere lightweight, flexibility, moderate conductivity and magneti-

ation are required. Deliberate modifications in chemical and superolecular structure of polymer matrix by incorporating nano-

erromagnetic particles can lead to the formation of conductingerromagnetic materials which can be suitably designed for highech applications. Among different conducting polymers, polyani-

ine has been chosen because of its unique structure, containingn alternate arrangement of benzene rings and nitrogen atoms.he polyaniline exists in four forms namely leucoemeraldine (fullyeduced form), emeraldine base (50% oxidized and 50% reduced

∗ Corresponding author. Fax: +91 11 25726938.E-mail address: skdhawan@mail.nplindia.ernet.in (S.K. Dhawan).

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254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2008.06.026

© 2008 Elsevier B.V. All rights reserved.

orm), pernigraniline (fully oxidized form) and conductive emeral-ine salt. In recent years much research attention has been paido the conducting polymer composites with one or more mag-etic materials so that polymer possesses both electrical as well asagnetic properties. For the absorption of electromagnetic radia-

ions, ferrites are incorporated in the polymers as they possess highagnetization values which make them useful at higher frequen-

ies [14–16]. Many attempts to produce the colloidal polyanilineomposite containing the ferrite have been made using the differ-nt charge carriers for doping the polymer [17–23]. However, theesultant polymer composites lose its conductivity and have lowagnetization value.Nanostructures of polyaniline-Fe3O4 nanoparticle composites

ere also prepared in the presence of �-naphthalene sulfonic acids a dopant that shows a magnetization value of 6 emu g−1 [24].S Patent 6,764,617 claims a formation of conductive ferromag-etic composition comprising sulfonated lignin or a sulfonated

olyflavonid or derivatives thereof and ferromagnetic iron oxidearticles [25].

The present work deals with electrochemical and chemicalxidative polymerization of the aniline with nanosized �-Fe2O3articles with dodecyl benzene sulfonic acid (DBSA) as dopant and

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amaitquent cycles, new oxidation peaks appear which indicates thatthese radical cations undergo further coupling to form benzenoidstructure and combination of benzenoid and quinoid structure.The peak current increases continuously with successive potentialscans to build up electroactive polyaniline on the electrode surface.

52 K. Singh et al. / Materials Chemi

eports the effect of �-Fe2O3 on the electrical, magnetic, dielectricnd shielding properties of the resultant conducting polyaniline--Fe2O3 nano-composite. Electrochemical studies were carried outsing cyclic voltammetric technique in order to see the incorpora-ion of �-Fe2O3 nanoparticles in the conducting polyaniline matrix.eside this, characterization of the polymer composite has beenarried out by FTIR spectroscopy, transmission electron microscopyTEM) and thermogravimetric analysis (TGA)

. Experimental

.1. Synthesis of the �-Fe2O3 nanoparticles

The magnetic nanoparticles of �-Fe2O3 were synthesized by coprecipitaionethod. The aqueous solution of 1.0 M FeCl2·4H2O and 2.0 M FeCl3 were mixed

ogether and precipitated by adding ammonium hydroxide solution with contin-ous stirring for 2–3 h by maintaining the pH at 10–11 [26]. The precipitated ferritearticles are filtered out and washed thoroughly with distilled water. �-Fe2O3 par-icles so obtained are dried at 120 ± 1 ◦C in vacuum oven. The formation of �-Fe2O3

anoparticles were confirmed by X-ray diffraction pattern.

.2. Synthesis of polyaniline composite with �-Fe2O3

Chemical oxidative polymerization of aniline was carried out in the presence ofanoferrite particles in aqueous medium. 0.3 M DBSA and �-Fe2O3 were homoge-ized by using the ART-Miccra D-8 (N0-10956) homogenizer at 10500 rpm for 2–3 h.o this 0.1 M of aniline (An) was added and supersonic stirring was continued forh to form an emulsion. The oxidant ammonium peroxidisulfate (0.1 M) was addedrop-by-drop keeping the temperature of the reactor at −2.0 ◦C with vigorous stir-ing for 5–6 h to the above emulsion. The green polymer precipitate so obtained wasreated with isopropyl alcohol under vigorous stirring for 2–3 h. The resulting pre-ipitate was then filtered and washed thoroughly and dried at 60–65 ◦C in a vacuumven. Several composition of the polymer composite having different weight ratio ofonomer to ferrite An:�-Fe2O3::2:1(PC21), 1:1(PC11), 1:1.5(PC115), 1:2(PC12) are

lso synthesized in DBSA medium to check the effect of ferrite constituents in theolymer matrix. Beside this, for comparison of results, polyaniline doped with DBSAPD13) without ferrite particles is also synthesized using emulsion polymerization.

.3. Electrochemical polymerization

The electrochemical polymerization of 0.1 M aniline in 0.3 M DBSA was car-ied out at 0.8 V on platinum electrode vs. SCE reference electrode. The polymerlm growth was also studied by cycling the potential between −0.20 and 0.95 V ont electrode at a scan rate of 20 mV s−1. Prior to polymerization, the solution waseoxygenated by passing argon gas through the reaction solution for 30 min. Elec-rochemical growth study of aniline in the presence of �-Fe2O3 particles were alsotudied on platinum electrode in DBSA medium.

.4. Characterization

The conductivity of the powder pellet of the sample polyaniline-�-Fe2O3 com-osite was measured by four-probe method using Keithley programmable currentource and nanovoltmeter attached to digital temperature controller and APD Cryoooler. The magnetic measurements of the ferrite as well as conducting PANI–�-e2O3 composite were carried out using vibrating sample magnetometer (VSM),odel 7304, Lakeshore Cryotronics Inc., USA. Thermogravimetric analysis of the

olymer and composite were carried on a Mettler Toledo TGA 851e. FTIR spectraere recorded on Nicolet 5700 and UV–vis absorption studies were carried on Shi-adzu 1601 Spectrophotometer. Three-electrode cell geometry was used in all the

lectrochemical experiments, where Pt was used as working electrode as well asounter electrode and SCE was used as reference electrode. An Auto lab PGSTAT30Ecochemie, Utrecht, The Netherlands) potentiostat/ galvanostat interfaced with aersonal computer was used in all the electrochemical measurements. The particleize and the morphology were examined using a Transmission electron microscopyTEM, JEOL JEM 1011) and the samples were deposited on carbon coated nickel grids.ermittivity and dielectric loss measurements were carried out on an Agilent E8362Bector Network Analyzer in a microwave range of 8.2–12.4 GHz (X-band), using5.8 mm × 7.9 mm × 6 mm copper sample holder connected between the waveg-ide flanges. To avoid air gap the above sample holder is modified with a groove of.5 mm on each side having 3 mm depth.

. Result and discussion

The emulsion polymerization of aniline to polyaniline in theresence of �-Fe2O3 particles may bring certain changes inhe properties of polyaniline because conduction mechanism in

FabS

d Physics 112 (2008) 651–658

olyaniline involves protonation as well as ingress of counternions in the polymer matrix to maintain charge neutrality. Pro-onation and electron transfer in polyaniline leads to formation ofadical cations by an internal redox reaction, which causes the reor-anization of electronic structure to give two semiquinone radicalations. In the doping process, ingress of anions occurs to main-ain charge neutrality in the resultant doped polyaniline matrix. Initu emulsion polymerization of aniline in the presence of �-Fe2O3onstituents resulted in the formation of ferromagnetic conductingolymer. In order to avoid phase segregation, the �-Fe2O3 nanopar-icles were functionalized with the surfactant DBSA that ensure itsompatibility with the polymer.

The electrochemical polymerization of aniline with DBSA inqueous medium was carried out using cyclic potential sweepethod by switching the potential from −0.20 to 0.95 V vs. SCE

t a scan rate of 20 mV s−1. The rise in current value at 0.78 Vn the first cycle corresponds to the oxidation of aniline leadingo generation of anilinium radical cations (Fig. 1). In the subse-

ig. 1. Electrochemical growth behavior of aniline in DBSA medium (PD13) andniline in DBSA medium containing ferrite particles (PC11) on cycling the potentialetween −0.2 and 0.95 V, taking eight successive scans, on platinum electrode vs.CE at a scan rate of 20 mV s−1.

K. Singh et al. / Materials Chemistry and Physics 112 (2008) 651–658 653

ons an

HpevmbctwtosTi

Plars1dop5wc

ma

ocoapabpwtptFsc[

˛

TC

S

PPPP�

Scheme 1. Mechanism for radical cati

owever when polymerization of aniline was carried out in theresence of �-Fe2O3 particles entrapped in the surfactant medium,lectrochemical growth behavior shows shifting of peak potentialalues, which indicates the incorporation of �-Fe2O3 in the poly-er backbone. Cyclic voltammogram of polyaniline film obtained

y potential sweeping technique in blank DBSA medium showsharacteristic peaks at 0.11, 0.44, 0.54 and 0.77 V (Fig. 2) due tohe generation of radical cations at 1st peak potential values whichere subsequently oxidized to dications [27] and represented in

he mechanism (Scheme 1). However, the cyclic voltammogramf polyaniline embedded with �-Fe2O3 particle in DBSA mediumhows characteristic peaks at 0.14, 0.48, 0.56 and 0.86 V (Fig. 2).he shifting of characteristic redox peaks can be assigned to thencorporation of �-Fe2O3 particles in the polyaniline matrix.

Fig. 3 shows the FTIR spectra of polyaniline doped with DBSA,C12 and �-Fe2O3.The main characteristics bands for the polyani-ine doped with DBSA are found at 1515 and 1458 cm−1 which aressigned for the C C bond stretching of quinoids and benzenoiding, respectively. Bands at 1257 and 1164 cm−1 are due to C Ntretching and in-plane bending of the C H bond while peak at024 cm−1 is due to −SO3H group. The peak at 1640 cm−1 may beue to the formation of the carbonyl group arising due to the over

xidation of the alkyl chain of the DBSA. In case of PC12, the maineaks are observed at 1034, 1123.1294, 1400, 1455, 1633, 630 and58 cm−1. The presence of the peaks at 630 cm−1 and 558 cm−1

hich are the characteristic band of Fe–O band stretching (Fig. 3,urve a) clearly indicate the presence of �-Fe2O3 in the polymer

wEapr

able 1onductivity, magnetization, UV–vis bands and dielectric properties of polyaniline and its

ample name � (S cm−1) Ms (emu g−1) Microwave p

Dielectric co

D13 2.11 – –C21 1.80 1.19 12.78C115 0.80 15.2 11.02C12 0.13 48.9 10.16-Fe2O3 10−7 69.8 6.32

d dications formation in polyaniline.

atrix while the shifting in the main peaks arises due to the inter-ction of the Fe2O3 with N-atom of the aniline ring.

Fig. 4 shows the UV absorption spectra of the different samplesf polyaniline and its composite with �-Fe2O3. The main peaks andalculated energy bands are shown in Table 1. Emeraldine base formf polyaniline in N-methyl pyrrolidione (NMP) shows two char-cteristic bands at 326 and 630 nm while the conductive form ofolyaniline doped with DBSA has shown the red shift to 353 nmnd 739 nm which were assigned to the �–�* transition of theenzenoid ring and polaronic transition respectively. But in case ofolyaniline composite, two changes were observed. First a blue shiftas observed for the band from 739 to 726 nm, which was ascribed

o polaronic transition. The reason behind this shifting may be theossible interaction of the �-Fe2O3 with polyaniline ring leadingo the formation of ferromagnetic composite. Second when the �-e2O3 content increases in different samples, absorption spectrahows the bathochromic shift for the band 353 to 349 nm. The opti-al band energy of the polymer was obtained from the given relation28]

h� = (h� − Eg)1/2 (1)

here ˛ is the absorption coefficient, h� is the photon energy andg is the optical band gap. The band gaps calculated by using thebove Eq. (1) varies from 1.45 to 1.49 eV and 2.87 to 2.75 eV for theolaronic transitions and �–�* transition of the benzenoid ringespectively.

composite with �-Fe2O3

roperties at 10.2 GHz Band gap (eV)

nstant εr Dielectric loss εr �–�* �*-polaron

– 2.82 1.459.13 2.78 1.497.82 2.75 1.496.77 2.75 1.470.29 – –

654 K. Singh et al. / Materials Chemistry and Physics 112 (2008) 651–658

Fig. 2. Cyclic voltammogram of polyaniline film in DBSA medium (PD13) and PANI-ferrite composite in DBSA medium (PC11) on Pt electrode vs. SCE at a scan rate of20 mV s−1.

Fig. 4. UV/Visible spectra of (�) EB, (�) PD13, (�) PC21, (�) PC115 and (�) PC12. Insets

lo((iwNaiainaicot

Fig. 3. FTIR spectra of (a) �-Fe2O3, (b) polyaniline-�-Fe2O3 com

hows the calculation of band gap plots in (˛h�)1/2 vs. photon energy (h�).

Fig. 5 shows the X-ray diffraction patterns of �-Fe2O3, polyani-ine doped with DBSA and it composite with different compositionsf �-Fe2O3. The main peaks for �-Fe2O3 are observed at 2� = 30.281d = 2.949 Å), 35.699 (d = 2.513 Å), 43.435 (d = 2.081 Å), 53.805d = 1.702 Å), 57.437 (d = 1.603 Å), 63.0460 (d = 1.473 Å) correspond-ng to the (2 0 6), (1 1 9), (0 0 12), (2 2 12), (1 1 15), (4 4 1) reflections

hich matches with the standard XRD pattern of �-Fe2O3 (PDFo. 25-1402). The peaks present in �-Fe2O3 were also observed inll the compositions of polyaniline composite with �-Fe2O3 whichndicates the presence of ferrite particles in the polymer matrixnd the intensity of peaks increase with the increase in the ratio ofron oxide. While the presence of polyaniline and its semicrystallineature is confirmed by the broad peaks at 2� = 19.795 (d = 4.481 Å)nd 25.154 (d = 3.537 Å) [29,30] and it is also observed that thentensity of these peaks increases with the decrease in iron oxide

omposite. The line broadening of the peaks in the entire patternsf polyaniline composite indicates about the small dimensions ofhe iron oxide particles. The crystallite size of �-Fe2O3 particle can

posite and (c) polyaniline doped with DBSA in KBr pellet.

K. Singh et al. / Materials Chemistry and Physics 112 (2008) 651–658 655

F(

b

D

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a

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ig. 5. X-ray diffraction plots of �-Fe2O3 (a), PC12 (b), PC11(c), PC21 (d) and PD13e) with arbitrary no of counts vs. 2�.

e calculated by line broadening using Scherer’s formula

= k�

ˇ cos �(2)

here D is the crystallite size for individual peak, � is the X-rayavelength, k the shape factor, D is the crystallite size for the indi-

idual peak of the crystal in angstroms, � the Bragg angle in degrees,nd ˇ is the line broadening measured by half-height in radians.he value of k is often assigned a value of 0.89, which depends oneveral factors, including the Miller index of the reflecting planend the shape of the crystal. The average size of �-Fe2O3 parti-les was calculated using above equation and estimated as 8.99 nmor pure �-Fe2O3 and 9.87 nm for polyaniline composite withron oxide having aniline: �-Fe2O3::1:2 (PC12) which is in accor-ance with the TEM analysis (Fig. 6) which shows the uniformly

ispersed iron oxide particles of 8–15 nm and the agglomer-ted polymer composite containing 8–13 nm size particles of ironxide.

Thermogravimetric analysis of the polyaniline doped with DBSAnd polyaniline composite was carried out in order to see the effect

Fig. 6. TEM image of �-Fe2O3 (a) and PC12 (b)

ftwas

ig. 7. Thermal gravimetric analysis of polyaniline doped with DBSA and polyanilineomposite with �-Fe2O3 with increasing content of �-Fe2O3; (�) PC12, (�) PC115,�) PC11, (�) PC21 and (�) PD13.

f the �-Fe2O3 content on the thermal stability of the compos-te (Fig. 7). Thermogram of different samples shows three major

eight losses, first at 100 ◦C due to the loss of water contents, sec-nd in the range of 230–380 ◦C due to the loss of the dopant fromhe polymer matrix and the third major loss from 380 to 700 ◦Cas attributed to the destruction of polymeric backbone. Polyani-

ine doped with DBSA (PD13) is thermally stable up to 230 ◦C.owever, when conducting polymer was synthesized by incor-orating ferric oxide moieties in the reaction system along withhe surfactant, it has been observed that the thermal stability ofhe polymer has increased to 260 ◦C. This shows that in situ poly-

erization of aniline in the presence of ferrite particles leads tobetter thermally stable conducting polymer. The approximate

mount of iron oxide for different polymer ferrite composites wasalculated by subtracting the residual weight of the blank polymer

having 8–15 nm size �-Fe2O3 particles.

rom residual weight of composite at 700 C. It is observed thathe for different compositions, PC21; PC11; PC115 and PC12 theeight percent of �-Fe2O3 is estimated to be 10.7%, 16.1%, 29.9%

nd 42.1% which is in accordance with the amount taken duringynthesis.

656 K. Singh et al. / Materials Chemistry and Physics 112 (2008) 651–658

F ng wiA

�cTdamllb[

�

we

T

a

R

wfTa�fI

vdipa0tcdtbtct

iTtoipo4A

ig. 8. Temperature dependence of conductivity of (a) PD13 (b) PC11 (c) PC12 alon/�-Fe2O3 ratio at 300 K.

The temperature dependent DC conductivity of the polyaniline--Fe2O3 composite having different weight ratio of ferric oxideontents were measured at temperature ranging from 50 to 300 K.he DC conductivity follows the semiconducting behavior andecreases with the decrease of temperature. The room temper-ture conductivity of the samples is shown in Table 1. Severalodels were used to explain the conductivity behavior in polymer

ike Arrhenius law and Mott’s equation. But it is observed that forow temperature range of 300–1.8 K the conductivity studies areest studies by the VRH model which follows the Mott’s equation31–34].

(T) = �O exp

[−(

TO

T

)1/�]

(3)

here TO is the Mott characteristic temperature and can bexpressed as

O = 8˛/kBN(EF)Z (4)

nd �O is the conductivity at T = ∞

= [˛ �/kBTN(EF)]−1/2 (5)

here ˛−1 is the localization length, which can be, determinedrom the magneto resistance data. From the observed values of

O and �O, one can calculate N (EF) density of states, R, the aver-ge hopping distance with the use of Eqs. (4) and (5). Exponentin Eq. (3) is the dimensionality factor having values 2, 3, and 4

or 1-, 2- and 3-dimensional conduction mechanisms, respectively.n this paper, we have plotted ln � vs. temperature with different

tvaon

th temperature from 50 to 300 K and (d) variation of conductivity with different

alues of � as 2, 3 and 4. It was observed that the conductivityata fits for the one dimensional VRH model with � = 2 with linear-

ty factor of 0.9996, 0.9997 and 0.9992 for the polyaniline (PD13),olyaniline-ferrite composite PC11 and PC12, respectively (Fig. 8)nd the corresponding value for 3D-VRH mechanism are 0.9933,.9962, 0.9956, respectively. The calculated values of the conduc-ivity (�) at room temperature are given in Table 1. The plot ofonductivity vs. the An/�-Fe2O3 (Fig. 8d) ratio shows that the con-uctivity decreases with the increase of ferrite constituent due tohe insulating nature of the �-Fe2O3 which hinder the flow of chargey blocking the conduction path in the polymer matrix. Thus fromhe above data, it is observed that 1D–VRH model is suitable for theonduction mechanism of the polyaniline-�-Fe2O3 composite andhe conductivity decreases with the increase of ferrite content.

The magnetic properties of the polyaniline-�-Fe2O3 compos-te and �-Fe2O3 were explained by using the M–H curve (Fig. 9).he saturation magnetization (Ms) value of the �-Fe2O3 was foundo 69.77 emu g−1 at an external field of 10 kOe having small valuef coercivity and negligible retentivity with no hysteresis loop,ndicating the super paramagnetic nature. When these nanoferritearticles are incorporated in the polyaniline matrix in weight ratiof 1:1(PC11) the magnetization saturation (Ms) value was found.13 emu g−1. However, on changing the weight composition ofn/�-Fe2O3 to 1:2, the Ms value was drastically increased from 4.13

o 48.9 emu g−1, keeping the external applied field at 10 kOe. The Ms

alues of different polyaniline-�-Fe2O3 composites was measurednd given in the Table 1. In all the cases very small coercivity isbserved with negligible retentivity which indicates the ferrimag-etic nature. Ms value increases due to high poly-dispersivity of the

K. Singh et al. / Materials Chemistry and Physics 112 (2008) 651–658 657

FPc

�t

o

F(

F(

ig. 9. Magnetization curves of (�) �-Fe2O3, (�) PC12, (�) PC115, (�) PC11 and (�)C21 showing the decrease in saturation magnetization with the decrease in �-Fe2O3

ontent.

-Fe2O3 in polyaniline matrix that arises due to the functionaliza-ion of nanoferrite particles with the surfactant DBSA.

The variation of complex permittivity of different samplesf polyaniline-�-Fe2O3 composite in the frequency range of

ig. 10. Real (�′) and imaginary (�′′) part of permeability of (�) �-Fe2O3, (�) PC12,�) PC115, (�) PC21 measured in X-band (8.2–12.4 GHz).

8ntTFpedd(f

S

wact(m

4

maasoswfdTtbripPPtt

ig. 11. EMI shielding effectiveness (SE) of �-Fe2O3 (�), PC12 (�), PC115 (�), PC21�) measured in X-band (8.2–12.4 GHz).

.2–12.4 GHz (X-band) are shown in Fig. 10. The real and imagi-ary part of permittivity (ε′

r and ε′′r ) of PC12 decreases from 12.1

o 9.7 and 7.6 to 4.5, respectively, with the increase in frequency.he minimum values of the dielectric losses propose polyaniline-�-e2O3 composite to be good shielding material [35]. The dielectricroperties are mainly due to interfacial polarization and intrinsiclectric dipole polarization which are partially attributed by theisordered motion of the charge carrier along the back bone of con-ucting polymer chain. The electromagnetic shielding effectivenessSE) of the � Fe2O3 and polymer composites was also measuredrom S-parameters as given below

E = −10 logPT

PI= −20 log

∣∣∣ET

EI

∣∣∣ = −20 log∣∣S21

∣∣ (6)

here PI (EI) and PT (ET) are the power (electric field) of incidentnd transmitted EM waves and |S21|2 is the transmission coeffi-ient, respectively. The maximum SE of −11.2 dB was recorded forhe sample PC21 while SE of −2.5 dB was observed for �-Fe2O3Fig. 11) proving that the polymer composite is better EMI shielding

aterial.

. Conclusion

Emulsion polymerization of the aniline with �-Fe2O3 in aqueousedium of DBSA leads to the formation of conducting super param-

gnetic polyaniline �-Fe2O3 composite with an Ms of 48.9 emu g−1

nd moderate conductivity of 0.13 S cm−1. Maximum dielectric con-tant value of 15.1 and shielding effectiveness of −11.2 dB wasbserved for the polymer composite for its application in EMIhielding and found to decrease with the increase in frequency. Itas observed that the variation of conductivity with temperature

or polyaniline and polyaniline-ferrite composite follows one-imensional VRH model with linearity factor of 0.9996 and 0.9997.he presence of �-Fe2O3 in the polyaniline matrix is confirmed byhe cyclic voltametry, as peak potential values of polyaniline shiftsy incorporation of ferrite particles in the polymer matrix. FTIResult has also shown the presence of characteristic band stretch-

−1

ng of Fe O band at 630 and 558 cm which clearly indicate theresence of �-Fe2O3 in the polymer matrix. Thermal stability ofANI-�-Fe2O3 composite is higher than the thermal stability ofANI-DBSA synthesized without �-Fe2O3. The enhancement in thehermal stability arises due to the presence of �-Fe2O3 particles inhe polymer matrix.

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58 K. Singh et al. / Materials Chemi

cknowledgements

Authors wish to thank Director N.P.L. for his keen interest inhe work. The authors also thank Dr. Hari Kishan, Dr. S.K. Haldernd Dr. R.P. Pant for carrying out low temperature conductivity andecording XRD data of our samples.

eferences

[1] K. Naishadham, IEEE Trans. EMC 34 (1992) 47, doi:10.1109/15.121666.[2] S.K. Dhawan, N. Singh, D. Rodrigues, Sci. Technol. Adv. Mater. 4 (2003) 105,

doi:10.1016/S1468-6996(02)00053-0.[3] R. Wycisk, R. Pozniak, A. Pasternak, J. Electrostat. 56 (2002) 55, doi:10.1016/

S0304-3886(01)00204-2.[4] S. Koul, R. Chandra, S.K. Dhawan, Polymer 41 (2000) 9305, doi:10.1016/S0032-

3861(00)00340-2.[5] Y. Wang, X. Jing, Polym. Adv. Technol. 16 (2005) 344, doi:10.1002/pat.589.[6] S. Koul, R. Chandra, S.K. Dhawan, Sens. Actuators B: Chem. 75 (2001) 151,

doi:10.1016/S0925-4005(00)00685-7.[7] A.D. Aguilar, E.S. Forzani, X. Li, N. Tao, L.A. Nagahara, I. Amlani, R. Tsui, Appl.

Phys. Lett. 87 (2005) 193108, doi:10.1063/1.2128038.[8] H. Yoon, M. Chang, J. Jang, Adv. Funct. Mater. 17 (2007) 431, doi:10.1002/

adfm.200600106.[9] W.H. Kim, A.J. Makinen, N. Nikolov, R. Shashidhar, H. Kim, Z.H. Kafafi, Appl. Phys.

Lett. 80 (2002) 3844, doi:10.1063/1.1480100.10] K. Fehse, G. Schwartz, K. Walzer, K. Leo, J. Appl. Phys. 101 (2007) 124509,

doi:10.1063/1.2748864.11] T. Dobbertin, O. Werner, J. Meyer, A. Kammoun, D. Schneider, T. Riedl, E.

Becker, H.H. Johannes, W. Kowalsky, Appl. Phys. Lett. 83 (2003) 24, doi:10.1063/1.1634688.

12] J.K. Lee, W.S. Kim, H.J. Lee, W.S. Shin, S.H. Jin, W.K. Lee, M.R. Kim, Polym. Adv.

Technol 17 (2006) 709, doi:10.1002/pat.766.

13] M. Al-Ibrahim, O. Ambacher, S. Sensfuss, G. Gobsch, Appl. Phys. Lett. 86 (2005)201120, doi:10.1063/1.1929875.

14] J. Qiu, H. Shen, M. Gu, Powder Technol. 154 (2005) 116, doi:10.1016/j.powtec.2005.05.003.

15] J.L. Kirschvink, Bioelectromagnetics 17 (1996) 187.

[

[

[

d Physics 112 (2008) 651–658

16] N.E. Kazantseva, J. Vilcakova, V. Kresalek, J. Magn. Magn. Mater. 269 (2004) 30,doi:10.1016/S0304-8853(03)00557-2.

17] G. Li, S. Yan, E. Zhou, Y. Chen, Colloids Surf. A: Physicochem. Eng. Aspects 276(2006) 40, doi:10.1016/j.colsurfa.2005.10.010.

18] M. Wan, J. Li, J. Polym. Sci. A: Polym. Chem. 36 (1998) 2799, doi:10.1002/(SICI)1099-0518(19981115)36:15<2799::AID-POLA17>3.0.CO;2-1.

19] G. Qiu, Q. Wang, N. Min, J. Appl. Polym. Sci. 102 (2006) 2107, doi:10.1002/app.24100.

20] S.E. Jacobo, J.C. Aphesteguy, A.R. Lopez, N.N. Schegoleva, G.V. Kurlyandskaya,Eur. Poly. J. 43 (2007) 1333, doi:10.1016/j.eurpolymj.2007.01.024.

21] W. Xue, K. Fang, H. Qiu, J. Li, W. Mao, Synth. Met. 156 (2006) 506,doi:10.1016/j.synthmet.2005.06.021.

22] L. Li, J. Jiang, F. Xu, Eur. Poly. J. 42 (2006) 2221, doi:10.1016/j.eurpolymj.2006.06.024.

23] M. Wan, W. Li, J. Polym. Sci. A: Polym. Chem. 35 (1997) 2129,doi:10.1002/(SICI)1099-0518(199708)35:11<2129::AID-POLA2>3.0.CO;2-T.

24] Y. Long, Z. Chen, J.L. Duvail, Z. Zhang, M. Wan, Physica B 370 (2005) 121,doi:10.1016/j.physb.2005.09.009.

25] Viswanathan, Tito, Berry, Brian, US Patent 6764617, 2004.26] R.M. Cornell, U. Schertmann, Iron Oxides in the Laboratory Preparation and

Characterization, second ed., Wiley, New York, 2000.27] D.E. Stilwell, S.M. Park, J. Electrochem. Soc. 135 (1988) 2254.28] F. Yakuphanoglu, E. Basaran, B.F. Suenkal, E. Sezer, J. Phys. Chem. B 110 (2006)

16908.29] M.G. Han, S.K. Cho, S.G. Oh, S.S. Im, Synth. Met. 126 (2002) 53,

doi:10.1016/S0379-6779(01)00494-5.30] T.D. Castillo-Castro, M.M. Castillo-Ortega, I. Villarreal, F. Brown, H. Grijalva, M.

Perez-Tello, S.M. Nuno-Donlucas, J.E. Puig, Composites: Part A 38 (2007) 639,doi:10.1016/j.compositesa.2006.02.001.

31] B. Sanjai, A. Raghunath, T.S. Natrajan, G.S. Rangarajan, P.V. Prab-hakaran, S. Thomas, S. Venkatachalam, Phys. Rev. B 55 (1997) 10734,doi:10.1103/PhysRevB.55.10734.

32] N.F. Mott, E.A. Davis, Electronic Processes in Non-Crystalline Materials, first ed.,Clarendon Press, Oxford, 1971.

33] N.F. Mott, Metal-Insulator Transition, second ed., Taylor and Francis, London,1990.

34] J. Joo, Z. Oblakowski, G. Du, J.P. Pouget, E.J. Oh, J.M. Wiesinger, Y. Min, A.G.MacDiarmid, A.J. Epstein, Phys. Rev. B 49 (1994) 2977.

35] S.W. Phang, T. Hino, M.H. Abdullah, N. Kuramoto, Mater. Chem. Phys. 104 (2007)327.