ORIGINAL PAPER

Polymer electrolyte nanocomposites with transition metaloxides’ nanoparticles

Puja Diwan & Amita Chandra

Received: 6 June 2013 /Accepted: 14 November 2013 /Published online: 23 November 2013# Springer Science+Business Media Dordrecht 2013

Abstract Polymer electrolytes nanocomposites based onpolyethylene oxide complexed with ammonium iodide anddispersed transition metal oxides (TMOs) nanoparticles havebeen prepared by the solution cast method. The electrical andmagnetic properties of the composites have been investigatedby impedance spectroscopy and vibrating sample magnetom-eter (VSM), respectively. The variation between the appliedmagnetic field intensity and the magnetization of the material(M-H curve) reveals that the iron oxide particles as well astheir composites show superparamagnetic behaviour at roomtemperature. These iron oxide dispersed composites have apotential to be used as medium field magnetic sensors.

Keywords Polymer electrolyte . Transitionmetal oxides .

Impedance spectroscopy . VSM

Introduction

The field of nanocomposites is exciting as these materialshave many applications. The challenge in developing nano-composites is to find ways to create macroscopic componentsthat benefit from the unique physical and mechanical proper-ties of very small (nano sized) particles within them.

The addition of inorganic fillers like SiO2, Al2O3, TiO2,semiconductors in the polymer-salt system generally im-proves the mechanical and transport properties alongwith the stability of the electrode-electrolyte interface[5,7,9,10,14,18,21–23]. Size of the particle plays an importantrole in the conductivity enhancement [6,8,12,16]. The role of

inorganic particle fillers in polymer electrolytes is to changethe recrystallization kinetics of the polymer chain and promoteamorphous regions, thus enhancing cation transport [3,11].

Recently, considerable research has been focused on mag-netic nano particles in various fields such as physics, medicineand biology due to their multi functional properties like smallsize, superparamagnetism and low toxicity [1,17,20].

Magnetic nanoparticles of transition metal oxides havegiven unique response to magnetic fields. They have a satu-ration magnetization much lower than that of their corre-sponding bulk materials. The matrix of magnetic nanoparti-cles with polymer electrolyte leads to the formation of mag-netic polymer composite possessing a unique combination ofboth electrical and magnetic properties that simultaneouslyinteract with both electrical and magnetic fields.

In the present study the polymer electrolyte compositescontain TMO nanoparticles as dispersoid. The aim of thisstudy is to demonstrate the influence of varying amounts ofmagnetic TMO nanoparticle on the electrical and magneticproperties of the magnetic nanocomposites. The amount of themagnetic filler is directly responsible for magnetic behaviourof obtained nanocomposites. It is expected that the combina-tion of polymer electrolyte and magnetic particles can form acomposite with electromagnetic properties.

Experimental

Synthesis of TMO nanoparticles and polymer electrolytenanocomposites

The TMO nanoparticles were prepared by different chemicalsynthesis methods;

Fe3O4 particles have been prepared by chemical precipita-tion method of FeCl2 and FeCl3 (1:2) molar ratio given by[19], Co3O4 have been prepared by thermal treatment of the

P. Diwan :A. Chandra (*)Department of Physics and Astrophysics, University of Delhi,Delhi 110007, Indiae-mail: achandra@physics.du.ac.in

J Polym Res (2013) 20:324DOI 10.1007/s10965-013-0324-0

precursor obtained via microchemical reaction ofCo(NO3)2.6H2O with NH4HCO3 by the method given by[24], NiO have been prepared by Nickel nitrate, nickel acetateand nickel chloride which have been used as nickel precursorto produce nickel oxide by the method given by [4] andMn3O4 have been prepared by ultrasonic-assisted synthesisat normal temperature and pressure describedby themethod given by [15]. These nanoparticles were dis-persed in the polymer electrolyte for preparing the poly-mer electrolyte nanocomposites.

The host polymer polyethylene oxide (PEO) and the saltNH4I were obtained from sigma Aldrich. Both PEO and NH4Iwere dissolved in distilled methanol and were stirred for3–4 h. When this polymeric complex solution became highlyviscous, then, it was poured into polypropylene petri-dishes.

The film was dried in room temperature for 7–8 days and thenwas further dried in vacuum (~10−3 Torr) for 2–3 h toeliminate all traces of the solvent. On the basis ofcomposition dependence of conductivity, the 90:10 ratio(NH4

+/EO=0.034) of PEO:NH4I was identified as thehighest conducting composition.

For making the polymer electrolyte composites, thedesired amount of TMO particles were dispersed in thePEO:NH4I (90:10) viscous solution. The TMO particleswere added in desired ratio (1–10 wt.%). For drying thefilms, the procedure described earlier was adopted. Vac-uum evaporated aluminium electrodes were used forelectrical contacts. While making electrodes, the cornersof the films were pasted on a mask with an adhesive toavoid shrinkage of the films. The solubility limit ofTMO nanoparticles in the polymer electrolyte was upto10 wt.% after which the films became brittle.

Instrumentation

For the magnetic measurements Microsens, ADE-ModelEV9 vibrating sample magnetometer was used to deter-mine the magnetic properties of the materials as afunction of the magnetic field.

The total electrical conductivity (σT) of the polymercomposite films was evaluated by complex impedancespectroscopy in the frequency range 1mHz to 100 KHz

Fig. 1 a Magnetization curve for transition metal oxide particles (insetshows the magnetization curve for Mn3O4, NiO, Co3O4 nanoparticles). bMagnetization curve for pure polymer electrolyte and TMO

nanocomposites.(inset shows the magnetization curve for polymer elec-trolyte and Mn3O4, NiO, Co3O4 nanocomposites)

Table 1 Saturation magnetization and magnetic nature of different TMOparticles

TMO SaturationmagnetizationMs (emu/g)

Magnetic natureof self standingTMO particles

Magnetic nature ofTMOnanoparticles

Fe3O4 51.8 Ferromagnetic Superparamagnetic

NiO 0.28 Antiferromagnetic paramagnetic

Mn3O4 0.22 Ferromagnetic paramagnetic

Co3O4 0.53 Antiferromagnetic paramagnetic

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by using HIOKI 3522–50 LCRHi Tester (error;∣Z∣ ±0.08%rdg. and θ ±0.05º).

TEM/EDAX was done by Technai G2 300 KV HRTEM.The XRD patterns of the samples were recorded using

Bruker D8 discover X-ray diffractometer at Cu-Kα radiationfor the Bragg angle (2θ) range from 10° to 80°.

The DSC was performed with TA Instruments, Model:Q100. The samples were put in Aluminum pan and the mea-surements were carried out from 25 °C to 250 °C at a heatingrate of 5°Cmin−1 in a static nitrogen atmosphere.

Results and discussion

Magnetic measurements

VSM studies have been done for the synthesized TMO nano-particles and the polymer electrolyte composites dispersed

with TMO nanoparticles. Figure 1a shows the M-H curvesfor different TMO nanoparticles. The parameters are given inTable 1 according to which, the saturation magnetization ofFe3O4 is highest as compared to other nanoparticles. Fe3O4

nanoparticles show superparamagnetic behaviour. For NiO,Mn3O4 and Co3O4 nanoparticles, M-H curve is linear with thefield having no coercivity at room temperature. Hysteresis inthe single-domain ferromagnetic particles vanish when theparticle size becomes small. Superparamagnetism is a formof ferromagnetism which occurs when the material is com-posed of very small crystallites ~ (1–15 nm). In this case, evenwhen the temperature is below the Curie or Neel temperature(and hence the thermal energy should not be sufficient toovercome the coupling forces between neighbouring atoms),the thermal energy is sufficient to change the direction ofmagnetization of the entire crystallite. The resulting fluctua-tions in the direction ofmagnetization cause the magnetic fieldto average to zero. Thus, the material behaves in a mannersimilar to paramagnetic materials. In this state, an externalmagnetic field is able to magnetize the nanoparticles, similarlyto a paramagnet, but their magnetic susceptibility is muchhigher than the paramagnets. Figure 1b shows the magnetiza-tion curves for the polymer electrolyte and its composites withdifferent TMO nanoparticles. The composite with iron oxideparticles also shows superparamagnetic behaviour but thevalue of saturation magnetization is low as compared to self-standing Fe3O4 particles. However, the value of the saturationmagnetization is high in comparison to other TMO

Fig. 2 XRD patterns of TMOnanoparticles

Table 2 Crystallite size of TMO nanoparticles

Transition metal oxides Crystallite sizeby XRD (nm)

Particle size distributionby TEM (nm)

Fe3O4 ~10 9–11

Mn3O4 ~11 11–15

NiO ~12 10–15

Co3O4 ~13 13–15

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nanocomposites which is due to the higher value of saturationmagnetization of iron oxide particles as shown in Table 1.

XRD studies

Figure 2 shows the XRD patterns of the TMO nanopar-ticles where the diffraction peaks are shown and aremarked by their indices. XRD has been done to identifythe crystal structure and determine the crystallite size ofthe magnetic nanoparticles, The diffraction pattern showsno peaks for any impurity suggesting that the productconsists of the pure phases of the materials. The crystal

structure of the nanoparticles has been found to be fccwhich is the same as that of bulk Fe3O4, NiO, Co3O4

and Mn3O4. The crystallite size of the magnetic particles(Fe3O4, NiO, Co3O4, Mn3O4) has been calculated usingthe Scherrer relation [13]

D ¼ Kλ=βCosθ ð1Þ

Here, the X-ray wavelength of CuKα radiation λ is 1.54A0, K is shape factor which is about 0.89. β is the full width athalf maximum in radians and θ is the Bragg angle. Table 2shows the crystallite size of TMO nanoparticles.

Fig. 3 TEM images of synthesized nanoparticles and corresponding EDX spectra

Fig. 4 a TEM image of ironoxide composite and (b)corresponding EDAX spectra

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TEM studies

Figure 3 shows the TEM images of the TMO nanoparticlesand their corresponding EDAX patterns. It can be seen that thesizes of the various nanoparticles are almost uniform and mostof the Fe3O4 nanoparticles are spherical in shape with themean diameters in the range from 9 to 11 nm whereas theMn3O4 nanoparticles are of ~11–15 nm, NiO particles havehexagonal shape and size around 10–15 nm while the Co3O4

nanoparticles have ~13–15 nm size. The TEM image of Fe3O4

particles shows aggregates due to their large surface area andmagnetic dipole interactions between the particles.

A change in the morphology of the polymer electrolyte hasbeen observed after dispersal of Fe3O4 particles. The disper-soid particles are uniform and well dispersed. Figure 4a and bshows the TEM images of the iron oxide composites. Fromthe micrograph, it is seen that the dispersed Fe3O4 particlesform a chain which form the percolation pathway for chargecarriers. Figure 4c shows the EDAX of composites containingFe3O4 nanoparticles. The Additional peak appearing in thespectrum has originated from the copper grid. Size distributionof the Fe3O4 nanoparticles and nanocomposites are shown in thehistogram (Fig. 5a and b). The histogram shows the averageparticle diameter of particles. The size of the Fe3O4 nanopartilcesis ~ 9–11 nm. However, in the composite, the size increasesto ~ 10–14 nm due to the agglomeration of these nanoparticleswhen dispersed in a highly viscous polymeric medium.

Ionic conductivity measurements

Figure 6 shows the variation of conductivity of compositeshaving TMO nanoparticles. In Fig. 6, it is seen that theconductivity of the iron oxide composite is highest as com-pared to the other TMO composites. Conductivity enhance-ment in the composites is because of the nanoparticles whichinduce the space charge layer at the interface between themagnetic particles and electrolyte. The variation of conduc-tivity is similar to other ion conducting polymer composites.According to the percolation theory proposed by [2], the ionicconductivity of the composites peaks at a threshold value ofthe concentration of the dispersoid, Fig. 2. The conductivity of

iron oxide composites is high due to the size effect because thesize of the iron oxide particles is small as compared to otherTMO nanoparticles. The size of the particle has been calcu-lated by TEM and XRD.

Another possibility for conductivity enhancement in thecomposites is due to the Lewis acid-base-type oxygen and OHsurface groups on the TMO nanoparticles which will interactwith the cations and anions and provide additional sites cre-ating favourable high conducting pathways in the vicinity ofthe nanoparticles for the migration of ions. This is reflected asan increased mobility for the migrating ions.

Because of their high conductivity and high satura-tion magnetization, the iron oxide dispersed compositeshave been chosen for further studies.

Magnetic properties of Fe3O4 dispersed nanocomposites

Figure 7 shows the room-temperature magnetization curves ofthe Fe3O4 dispersed nanocomposites. The values ofMS for the

Fig. 5 Histogram correspondingto the TEM image of the (a)Fe3O4 nanoparticles and (b)polymer electrolyte compositeswith dispersed Fe3O4

Fig. 6 Variation of conductivity of TMO nanocomposites

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composites are in the range 0.5–3.5 emu/g, increasing with theincrease in the Fe3O4 content. These nanocomposites do notshow hysteresis loop. Lower values for the saturation magne-tization have been obtained for the Fe3O4 dispersed compos-ites in comparison to the Fe3O4 particles due to the smallamount of iron oxide particles (1–10 wt.%) that have been

dispersed into the polymer electrolyte giving mechanicallystable films. The superparamagnetic behaviour of Fe3O4 par-ticles in the investigated composites is evidenced by theabsence of the hysteresis loop in the magnetization curvesfor all the composite samples.

Fig. 7 Composition dependenceof saturation magnetization ofiron oxide dispersednanocomposites

Fig. 8 DSC thermograms of (PE) polymer electrolyte and Fe3O4

dispersed nanocomposites Fig. 9 Variation of conductance of Fe3O4 nanocomposites

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Thermal studies

Figure 8 shows the DSC thermograms of the polymer electro-lyte and the polymer electrolyte-Fe3O4 composites. The en-dothermic peaks which correspond to the melting temperature(Tm) of the PE/composites shifts to lower temperatures and thepeaks become broad on the incorporation of Fe3O4 indicatingenhancement in the amorphous phase which results in ionicconductivity enhancement.

Effect of magnetic field on the conductance of Fe3O4

dispersed composites

Figure 9 shows the variation of conductance in the presence ofmagnetic field of Fe3O4 dispersed composites. As the magnet-ic field is gradually increased, the value of the conductancestarts decreasing since, due to the application of the magneticfield, the magnetic dipoles start moving in the field directionand as a result of alignment in the field direction, their numberbecomes lesser as the applied field intensity increases. There-after, the conductance attains a constant value as the appliedmagnetic field saturates the alignment of magnetic dipoles ofthe TMOnanoparticles. These results demonstrate themagneticfield assisted rearrangement of molecular domains. This varia-tion shows the potential of this nanocomposite as a mediumfield (1μG to 10G) magnetic sensor. This being the first studygiving a direction to proceed, now, a detailed study with inter-mediate compositions and magnetic fields is being undertaken.

Conclusion

Polymer electrolyte nanocomposites have been synthesizedby dispersing TMO nanoparticles in PEO:NH4I by solutioncast method. Out of the four nanocomposites, Fe3O4 dispersednanocomposites are the best nanocomposites due to theirmagnetic and electrical properties. These nanocompositesshows superparamagnetic behaviour with electrical conduc-tivity of ~10−5 S/cm at RT. The magnetic property of thecomposites depends upon the amount and saturation magne-tization of the magnetic dispersoid particles. These compos-ites can be developed into medium field magnetic sensors.

Acknowledgments Authors gratefully acknowledge the financial sup-port received from the University Grants Commission (for researchfellowship), DST & University of Delhi (for grant of funds) and USIC,Delhi University (for providing experimental facilities).

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